“I do theme reviews for the theme repository on WordPress.org. All the code and assets in the theme need to be GPL compatible. I have a few questions about how GPL compatible images work with model releases. The popular GPL compatible image licence is CC0.
- Can an image be released under CC0 even if there is no model release?
- Is a CC0 image without a model release GPL compatible?
- Who is responsible for getting the model release? The photographer, theme author, website owner?
- Who is liable if a theme with a CC0 image without a model release is used on a pornographic site?”
Thanks for the great bunch of questions Ulrich. I appreciate receiving them.
Outline and summary
Before I jump into the specific questions you’ve raised, I think it may be helpful for some people if we step back from those questions and:
- sketch out what WordPress.org and the Theme Review Handbook have to say about GPL-compatibility;
- describe CC0;
- analyse what is meant by “GPL-compatibility”; and
- explain why, in my view, CC0 is considered to be GPL-compatible.
After that, I’ll address your specific questions. I’ll also make some (potentially controversial) comments on CC-BY / CC-BY-SA and GPL compatibility.
This is fairly long post as it covers quite a bit of ground. Bearing in mind that some people might just want some quick answers, here’s a quick summary:
Summary of ‘Theme reviews, CC0, model releases and GPL-compatibility’
Repository themes and GPL-compatibility: WordPress.org and the Theme Review Handbook say that a theme submitted to the WordPress.org repository must be 100% GPL-licensed or use a GPL-compatible licence. However, what this means in the context of theme submission and review is not entirely clear from WordPress.org and the Theme Review Handbook themselves.
CC0: CC0 is a Creative Commons tool which enables a copyright owner to waive copyright in a work and, if that’s not effective in a given country, it falls back to a very broad and obligation-free licence.
WordPress theme reviews and GPL-compatibility: In my view, when referring to “GPL-compatibility”, the WordPress theme review pages can be taken to be referring to the Free Software Foundation’s meaning of that term.
Free Software Foundation’s approach to GPL-compatibility: The Free Software Foundation (FSF) explains that, if two programs’ licences permit the programs to be combined into a larger work, they are compatible. If there is no way to satisfy both licenses at once, they are incompatible. The FSF also explains that another (non-GPL) licence is compatible with the GPL if it permits the combination of programs (derivative work) to be released under the GPL. On my understanding of the FSF’s approach, it doesn’t matter that there is no obligation in the non-GPL licence or mechanism, that applies to the component(s) being added to the GPL’d work, to license a derivative work based on that or those component(s) on the same (or any) terms. The key question is whether the GPL can be applied to the combination or end product. CCo is considered to be GPL-compatible because it meets this requirement.
Releasing CC0’d images without a model release: An image can be released under CC0 even if there is no model release. However, care may still be required in relation to third party rights that are not (and cannot be) waived or licensed under CC0, particularly where an identifiable person appears in the image or the image is of copyright protected property such as another photo or artwork. This is because the totality of rights involved is greater than copyright alone.
CC0’d image without model release and GPL-compatibility: Whether a CC0’d image without a model release is compatible with the freedoms under the GPL depends, in my view, on (a) the nature of the image; and, if the image is of an identifiable person or separate copyright protected property (such as an artwork), (b) whether any uses could infringe the person or copyright owner’s rights. If the answer to (b) is yes, it would be challenging to say the CC0’d image is compatible with the GPL’s freedoms because there will likely be significant constraints on its re-use.
Who should get the release? Where a model or property release is required, the most obvious party to obtain the release is the photographer. In many cases it may be difficult for theme authors or website owners to obtain a release because they might not know who to contact. This doesn’t mean, however, that the only ‘legal responsibility’ is on the photographer. A theme author or website owner who uses a CC0’d image in circumstances where a model or property release is required, but where one hasn’t been obtained, may still be on the hook.
The pornographic site question: Turning to the pornographic site question, the short answer is that the person responsible for using the image on the pornographic site, usually the site owner, will be the one directly in the firing line because that person will have published the image on the site.
CC0 and model releases: There is an interesting question about the nature of the model release that would be required for an image of an identifiable person that is released to the public domain under CC0. The release would need to be very broad. The standard kind of release one finds on a range of photography and other websites wouldn’t cut it. Given the popularity of Unsplash, I discuss this and related issues in the context of that (super helpful) site.
CC-BY and CC-BY-SA images for themes: The potentially controversial bit I mentioned above is this: assuming that the rationale of WordPress.org’s focus on GPL-compatible licensing is on ensuring that the GPL is complied with and that people’s use of themes is not constrained, arguably certain other open licences could be used for image files included with a theme for the WordPress.org repository, such as CC-BY and CC-BY-SA. There is obvious value in this given the wealth of CC-BY and CC-BY-SA licensed images. (This one takes a bit of explaining; please read the explanation below before jumping to conclusions and shooting me down.)
Decision is one for the theme review team: Whether the WordPress.org theme review team wishes to open up the option of allowing CC-BY and CC-BY-SA images to be included in themes is a question for it. Additional guidance would be needed in the Theme Review Handbook, so as to help theme authors go about things correctly and help theme reviewers with what they should be looking for, but that wouldn’t be too challenging.
The remainder of this post explores these points in more detail.
Theme reviews and GPL compatibility
A Theme Review page on WordPress.org has this to say about licensing:
“Licensing, Theme Name, Credit Links, Up-Sell Themes:
- Themes are required to be licensed fully under a GPL-compatible license. [This reference to “a” GPL-compatible licence needs to be compared with, and arguably is qualified by, the “Bundled Resources” paragraphs below.]
- Themes are required to use appropriate Theme Names.
- If used, credit links are required to be appropriate.
- Guidelines: Licensing, Theme Name, Credit Links, Up-Sell Themes”
The Guidelines link takes you to a page by that name in the Theme Review Handbook. That page has this to say on licensing (the page is said to be deprecated but, when I wrote this, the page to which it links was virtually empty):
Theme License: #
- Themes are required to be 100% GPL-licensed, or use a GPL-compatible license. This includes all PHP, HTML, CSS, images, fonts, icons, and everything else. The complete theme must be GPL-Compatible.
- Themes may optionally include a full-text license, referenced as license.txt, or else link to a reasonably permanent URL that contains the full-text license.
- Themes are required to declare their license explicitly, using the License and License URI header slugs to style.css:
License: GNU General Public License v2.0
License URI: http://www.gnu.org/licenses/gpl-2.0.html
- Themes are required to declare copyright and license information as specified by the applicable license, e.g.:
Twenty Fourteen WordPress Theme, Copyright 2014 WordPress.org
Twenty Fourteen is distributed under the terms of the GNU GPL
- Derivative Themes are required to retain/declare the copyright information of the original work
Bundled Resources #
- Themes are required to state the copyright and license information for any bundled resources (e.g. PHP, CSS, JS, fonts and images) not covered by the Theme’s license statement.
- Themes are required to state the copyright and license information for any bundled resources not covered by the Theme’s license statement [this duplication is in the original]. Themes are recommended to state this information in the Theme’s README documentation.”
The key passages for present purposes are these:
Themes are required to state the copyright and license information for any bundled resources (e.g. PHP, CSS, JS, fonts and images) not covered by the Theme’s license statement.
I’m told that the popular GPL compatible image licence is CC0. It’s worth making a few comments about CC0 and asking the question: what makes a licence GPL-compatible and why is CC0 considered to be GPL-compatible? I think this is worthwhile because there has been a quite a bit of debate on these issues in WordPress theme review circles.
CC0 is not primarily a licence. It’s a tool that seeks to enable an owner of copyright in a work to waive the copyright in that work, thereby freeing it of copyright-related restrictions on re-use and releasing it into the public domain. It also states that, if or to the extent that the waiver is legally ineffective in a given country, an extremely broad and obligation-free licence is granted instead; this is generally known as the ‘licence-fallback’. So the tool, in essence, is a waiver + licence fallback.
Now, what makes CC0 GPL-compatible? Well, it depends on what one means by “GPL-compatible”.
GPL-compatibility not based on existence of share-alike obligation in non-GPL licence
As you’ll know, if you distribute a derivative work based on GPL’d code, the GPL requires you to license your derivative work under the GPL. The CC0 waiver/licence does not require any such thing. If the waiver part is effective in the country where it’s used for a copyright image (which is believed to be the case in the United States but perhaps not in countries like the United Kingdom, Australia and New Zealand), copyright in the image is completely waived and the work is essentially thrust into the public domain. In the absence of copyright in the image, anyone that gets their hands on the work can – from a copyright perspective – do whatever they want with the image (there might be other restrictions based on other areas of law, but we’ll park that for now). For example, they can adapt it to their heart’s content without any obligation to license it on any terms at all if they distribute it. For most practical purposes, the same position prevails if the waiver is ineffective and the licence fallback kicks in.
We can see, then, that CC0 is not a copyleft device like the GPL because CC0 contains no ‘downstream licensing of derivative work’ requirement.
What meaning is the WordPress theme review crew applying?
So, what’s going on here? If, by GPL-compatible, one means freedoms and obligations equivalent to those in the GPL, then CCO is clearly not compatible. However, that can’t be the intended meaning in the Theme Review Handbook because CC0 is considered to be GPL-compatible. So how do we find the actual meaning, particularly when the Theme Review Handbook doesn’t define what it means by “GPL-compatible”? I think (and please Theme Review Team tell me if I’m wrong) that the intended meaning is that which the Free Software Foundation (the guardian of the GPL) gives to the term.
There are at least two places to look on the GNU website where the GPL lives. First, an FAQ page answers two questions relating to licensing compatibility, one in general terms and the other relating to GPL-compatibility:
“What does it mean to say that two licenses are “compatible”?
In order to combine two programs (or substantial parts of them) into a larger work, you need to have permission to use both programs in this way. If the two programs’ licenses permit this, they are compatible. If there is no way to satisfy both licenses at once, they are incompatible.
For some licenses, the way in which the combination is made may affect whether they are compatible—for instance, they may allow linking two modules together, but not allow merging their code into one module.
Just to install two separate programs in the same system, it is not necessary that their licenses be compatible, because this does not combine them into a larger work.
What does it mean to say a license is “compatible with the GPL?”
It means that the other license and the GNU GPL are compatible; you can combine code released under the other license with code released under the GNU GPL in one larger program.
The GPL permits such a combination provided it is released under the GNU GPL. The other license is compatible with the GPL if it permits this too.”
The second place to look is the GNU website’s list of Various Licenses and Comments about Them. This is what it says about CC0:
CC0 is a public domain dedication from Creative Commons. A work released under CC0 is dedicated to the public domain to the fullest extent permitted by law. If that is not possible for any reason, CC0 also provides a lax, permissive license as a fallback. Both public domain works and the lax license provided by CC0 are compatible with the GNU GPL.
If you want to release your work to the public domain, we recommend you use CC0.”
From all this it is fairly clear what the FSF has in mind when referring to GPL compatibility. The key question in its mind is whether the GPL can be applied to the combination of GPL-licensed code and non-GPL licensed code. The non-GPL licence must allow this and it must not impose restrictions that are inconsistent with the GPL’s freedoms. It doesn’t matter that there is no obligation in the other, non-GPL licence or mechanism, that applies to the component(s) being added to the GPL’d work, to license a derivative work based on that or those component(s) on the same terms of the non-GPL licence (or indeed under any licence). The key question is whether the GPL can be applied to the end product.
CC0 (at least in its waiver form) ticks these boxes and this is why, in my view, the Free Software Foundation considers it to be compatible with the GPL. In particular:
- the rights CC0 confers are broader than those in the GPL;
- CC0 is less onerous than the GPL (there are no copyright-related obligations at all if the waiver is effective); and
- looking at it from a code perspective for now, where GPL’d and CC0’d code are combined to form a derivative work, that derivative work as a whole can be licensed under the GPL. Note that doing this doesn’t bring copyright in the CC0’d portions back from the dead (in cases where the waiver was effective). Rather, the GPL comes to apply to any new original element comprised in the derivative work. (This is not the same as saying the originally granted GPL licence is extended; rather, the new component is likewise but separately GPL-licensed such that all copyright parts of the resulting code are GPL-licensed.)
I suggest that the above meaning of “GPL-compatibility” be recognised in the Theme Review Handbook so as to avoid further debate as to what this otherwise ambiguous term means. (This isn’t legal advice, of course. It’s just a suggestion and one people might want to stress test, whether with the community and/or other lawyers.) I’m going to make a qualification to this further below that suggests a distinction might be draw between code and images but, before doing that, I’m going to answer Ulrich’s specific questions.
Can an image be released under CC0 if even there is no model release?
To understand this question and its answer one needs to understand what a “model release” is and why one may be required in some circumstances. It’s actually easier to start with the second question first.
A potentially broad range of rights
You might think that a photographer who owns the copyright in an image (which they often will do under their contracts with customers) could do whatever he or she likes with it. In many cases that will be true but the position needs to be qualified where an identifiable person appears in the photo, particularly if that person commissioned the photo or the photo is somehow private in nature. This is because, in such circumstances, the totality of rights involved may be greater than just copyright.
Depending on the circumstances and the country’s laws that apply, the person in the photo may have privacy rights, the right to be shown in the photo in a particular manner, contractual rights in his or contract with the photographer (if there is one), character merchandising rights, publicity rights and/or other rights to control one’s own image or personality (this last one being more common in civil law jurisdictions).
For example, photos taken in a person’s home or on some other private property may be private in nature and, in some countries, even photos taken of a person in a public place have the potential to be private in nature if, for example, the photos were obviously private or their publication could be offensive in some other way. And particular care needs to be taken with photographs of children (on this point see the United Kingdom Court of Appeal’s decision in a case involving the taking of JK Rowling’s child when the family was out for a walk in the street: Murray v Big Pictures (UK) Ltd  EWCA Civ 446). It is important to emphasise too that the relevant rights and the circumstances in which consent is required differ from jurisdiction to jurisdiction.
The kinds of rights referred to above will, when they exist, often limit the circumstances in which a photo of a person can be used, even where in a given country the photographer is the copyright owner.
This is the main reason for so-called “model releases”, or “image releases” as they are also known. They serve two main purposes: obtaining the relevant permissions from the subject of the photo and protecting the photographer (and potentially other users depending on the breadth of the release) from liability in relation to any use that falls within the scope of the release. In essence, a model release allows certain specified uses and releases the authorised person(s) from liability in relation to those uses. You can find some examples of model releases here and here.
It is also important to note that there is a separate category of release called a “property release”. This serves the same kind of purposes as a model release but is used where a photo is taken of an item of property that itself is protected by copyright (or a similar or related right) where the taking of the photo either does or could amount to infringing copyright (or the similar or related right) in the subject of the photo. The most obvious examples are where someone takes a photo of a copyright photo, artwork or business logo. You can find some examples of property releases here and here.
Back to the question
With all that in mind, let’s now return to the first question: Can an image be released under CC0 even if there is no model release? The short answer is yes but it’s important to understand why. The answer is yes because CC0 is only dealing with the “Affirmer’s” “Copyright and Related Rights”. The “Affirmer” is the person who is who associating CC0 with the work. “Copyright and Related Rights” is defined to include “publicity and privacy rights pertaining to a person’s image or likeness depicted in a Work” but the Affirmer is only waiving (or licensing under the fallback) his or her or its own “Copyright and Related Rights”. Third party rights that may exist are beyond the scope of CC0. CC0 states in clause 4(c):
“Affirmer disclaims responsibility for clearing rights of other persons that may apply to the Work or any use thereof, including without limitation any person’s Copyright and Related Rights in the Work. Further, Affirmer disclaims responsibility for obtaining any necessary consents, permissions or other rights required for any use of the Work.”
So, while the answer to this question is yes, it’s not the fully story. The full story is: yes, but care may still be required in relation to third party rights that are not (and cannot be) waived or licensed under CC0, particularly where an identifiable person appears in the image or the image is of copyright or similarly protected property such as another photo or artwork.
Is a CC0’d image without a model release GPL compatible?
In my view the answer to this is: it depends. If the image is of, for example, nature scenes, groups of people whose faces can’t be seen and who can’t otherwise be identified, general everyday objects and anything else in which there is no separate copyright or other third party rights, then the answer will probably be yes. In these circumstances it is unlikely that there’ll be any restraints or prohibitions that conflict with the freedoms conferred by the GPL.
By contrast, if the image is of a person or copyright property (e.g., an artwork) for which no release has been obtained when one should have been obtained, then the answer is probably no. The answer is no because the absence of the relevant release either may or will mean that a component of the theme files (some or all of an images folder) cannot be used to the same extent that the other components can under the GPL.
Who is responsible for getting the model release? The photographer, theme author, website owner?
Where a model or property release is required, the most obvious party to obtain the release is the photographer. All major stock photo suppliers, like iStock, Shutterstock and Bigstock, require this of their contributing image suppliers. In some cases it may be difficult for theme authors or website owners to obtain a release because they might not know who to contact.
This doesn’t mean, however, that the only ‘legal responsibility’ is on the photographer. If a theme author or website owner uses a CC0’d image in circumstances where a model or property release is required but the photographer didn’t obtain one (and the theme author or website owner didn’t obtain one), the subject of the photo (if a person) or the owner of the infringed copyright (e.g., an artwork) may still have legal rights against the theme author or website owner.
Who is liable if a theme with a CC0’d image without a model release is used on a pornographic site?
This question (I think) is really focusing on CC0’d images of people for which a model release has not been obtained. It also raises an interesting issue about the breadth of release that would be required.
The short answer is that the person responsible for using the image on the pornographic site, usually the site owner, will be the one directly in the firing line because that person will have published the image. If the subject of the photo finds out that his or her image was bundled with the theme, then he or she might also have a crack at the theme author or photographer but what rights he or she might have would depend on the circumstances.
If the theme author or photographer had said the widest possible release was obtained (that would allow such use) when no such release was obtained, then the theme author or photographer might be the subject of complaint from the pornographic website owner if that person suffers loss as a result, but I suspect the likelihood of that fact scenario will usually be low.
CC0 and model releases | Unsplash as a case study
The “interesting issue” I’ve mentioned above is worth discussing and it may help to explore it by reference to a live site where photos are available under CC0.
Broad release required
Where a photographer takes a photo of a person and wishes to obtain a model release that’s commensurate with CC0, the model release would need to be on the broadest of terms. Given the unrestrained uses that CC0 appears to grant users (who will have no idea whether all relevant releases have been obtained and who may put an image to any conceivable use), the photographer may well wish to obtain such a release so as to protect itself and/or ensure the photo subject is comfortable with the broad range of potential uses. Alternatively, the photographer may need to obtain such a release under the laws of the photographer’s country or a contract or other arrangement the photographer has with the subject may expressly or impliedly limit publication rights.
Informed consent required
The person who’s the subject of the photo would need to understand that the photo will be released into the public domain (or licensed on the widest of terms if the licence fallback kicks in) and that, once that occurs, anyone who obtains it may well and understandably think they can do more or less whatever they want with it, including – for example – selling it on t-shirts and using it on less-than-salubrious websites. In such cases the photo subject would, as a minimum, need to understand and consent to that.
Do all photographers know all this?
Unsplash as an example
I’ll take Unsplash as an example but I’m really not meaning to put any particular spotlight on it. I’m only choosing that site because it has been referred to in WordPress theme review discussions and because, in my view, it’s an awesome and hugely popular site. Some of the photographic talent on there is mind-blowing, I love the service it provides and its operators appear to take copyright and related rights seriously.
“… you represent and warrant that: (i) you either are the sole and exclusive owner of all Pictures that you make available through the Website or you have all rights, licenses, consents and releases that are necessary to grant to Company the rights in such Pictures, as contemplated under this Agreement; and (ii) neither the Pictures nor your posting [etc of them]… will infringe [among many other things]… a third party’s … rights of publicity or privacy… .”
A photographer that doesn’t yet know much about copyright law and model releases may not understand the full meaning of this clause. Its reference to “releases” exists among a number of similar terms, its reference to “rights of publicity or privacy” may not be understood and, as far as I can see, there are no FAQs on the site. At the same time, site users are told:
“Free (do whatever you want) high-resolution photos.”
That’s a potentially risky mix.
Risks if a contributing photographer gets it wrong
Similarly, users who publish the image on their own sites might find themselves on the end of, at least, a “please remove immediately…” request.
I should emphasise that I’m only talking about model releases here (i.e., in relation to photos with identifiable individuals) as that’s the subject of this post. You don’t need either a model release or a property release for the vast, vast (did I say vast?) majority of photos on Unsplash. In that vast majority of cases, there should be no issue as long as the contributing photographer owned the copyright or was authorised by the copyright owner and acted on its behalf in releasing the image under CC0.
Unsplash and model releases
Turning to whether model releases are relevant to Unsplash, I’ve seen some people suggest that there aren’t many headshots on Unsplash but that’s just not the case. You need to dig a little to find them (as very few appear when you scroll down the homepage) but they are certainly there. Here’s an example of one of the many beautiful people photos taken by David Olkarny:
There are many others on Unsplash by a range of photographers.
Would the subjects of any them mind if their images were to appear on t-shirts, mugs, prints, in magazines, newspapers, advertisements or less-than-salubrious websites? And if they did mind, would they have legal rights enforceable against the photographer and/or anyone that publishes them or at least uses them in certain ways? There’s no way I can know, of course, but I’d be pleasantly surprised if every photographer contributing such photos obtained a model release, when they needed to, that is as broad as the rights available when CC0 is applied to an image.
Unsplash appears to be vigilant
It may well be that Unsplash is extremely vigilant about these things. Again, I don’t know, although it does seem from WordPress theme review discussions in which an Unsplash founder has participated that they do take photo rights verification seriously.
What we do know, as I’ve noted above, is that site users are told:
“Free (do whatever you want) high-resolution photos.”
(As an aside, Unsplash certainly appears to be more vigilant than Pixabay, whose terms of service state that “Pixabay does not require a written Model Release for each Image that has identifiable people on it”.)
Bringing it back to CC0’d images of people in themes for WordPress.org
Placing this in the context of themes submitted to WordPress.org that contain CC0 images and considering now all potential sources of such images, one cannot discount the risk that, where the image files include photos of identifiable people (or property for which a property release may be required), there is a risk that not all required model (or property) releases have been obtained. If they haven’t been obtained, and sometimes depending on the nature of the photos and the circumstances in which they were taken, users of the themes may be at risk if they too publish the photos.
(A cynic might say that this is really no different to the risk that the user of any open source CMS takes by installing and running the open source codebase, the argument being that it too could contain third party copyright code that shouldn’t have been incorporated into the CMS. In a sense, that’s true, but it’s much easier to spot an image of a person on an unscrupulous site, for example, than it is to spot a few lines of code among thousands and thousands of lines.)
CC-BY / CC-BY-SA and GPL compatibility
A potential qualification
Earlier in this post I set out what I think “GPL-compatibility” means and I suggested that that meaning be recognised in the Theme Review Handbook so as to avoid further debate as to what this otherwise ambiguous term means. I also said I was going to make a qualification to this further below that suggests a distinction might be drawn between code and images. I’m now going to make that qualification.
The suggested meaning for the GPL-compatibility test is all well and good as far as it goes, but it doesn’t address the situation:
- where different types of files (e.g., code and images) can be combined without creating a derivative work; and, in that situation
- where the rationale for WordPress.org requiring GPL-compatible image files is not put in jeopardy if an alternative open licence is used for the images.
In other words, it doesn’t address the situation where the GPL-compatibility test is not met – in relation to images – but where, arguably, this doesn’t matter.
This is the situation I’d now like to explore. But first, a health warning: given what I’ve read in the theme review discussions, what I’m about to say may be controversial and it might give you a headache. Here we go… .
Themes and the status of images
In its opinion on WordPress themes and the GPL, the Software Freedom Law Center appears to have treated image files (among others) as independent works that are, to paraphrase GPL v2, merely aggregated with the software on a volume of storage or distribution medium; for this reason, they do not need to be licensed under the GPL if their owners/contributors prefer not to.
If they are separate, independent files (they are really a form of data), one might argue that they are beyond the rationale and scope of what I consider to be the Free Software Foundation’s GPL-compatibility test (on which I think the theme review team relies) because they would not need to be part of a “derivative work” based on either the WordPress core’s or a theme’s software. Rather, they would be (or could be in the right conditions) part of a compilation that would comprise the derivative work, the image files and any other independent copyright files. The significance of this is that, if they are not part of a derivative work, then they are not caught by the GPL’s viral/propagation requirement and GPL-compatibility is not required of them. To put it another way, if someone were to make a derivative work of the GPL’d software in a theme file on WordPress.org, the ‘downstream GPL licensing of derivative works’ requirement would not apply to the images (unless they’d been separately and expressly licensed under the GPL in their own right). They could be included in the new theme files under their original licences (assuming those licences were broad enough to allow re-use by others).
Using CC-BY and CC-BY-SA images in themes
On this line of argument, and assuming that the focus of WordPress.org’s licensing concern is on ensuring that people’s use of themes is not constrained, other licences could be used for image files included with a theme for the WordPress.org repository, such as CC-BY and CC-BY-SA. There is obvious value in this given the wealth of CC-BY and CC-BY-SA licensed images. In my view this wouldn’t be inconsistent with the open sharing community norm I’ve referred to in an earlier post. To the contrary, it would be entirely consistent with it. (Some might say only CC-BY-SA would be consistent, given its share-alike requirement but, in the case of images, I really don’t think that matters.)
One might object that it would be difficult for theme users to comply with the attribution requirements in these licences but I don’t think this is fatal because guidance could be provided in a readme file as to the various ways in which this could be done (e.g., in image captions or in the site footer or in a separate credits page linked to from the site footer). It would be the user’s responsibility to comply with the relevant CC licence. Bear in mind, also, that a licensor of a Creative Commons-licensed image can waive the attribution requirements if it wishes.
Another objection I’ve seen in discussions on WordPress.org about image compatibility is that licences like CC-BY and CC-BY-SA do not confer a right on licensees to sublicense the licensed work. The argument is that this is fatal to GPL-compatibility because, to license the images under the GPL, the Creative Commons licences would need to authorise that form of sub-licensing (because it’s distinct from the Creative Commons licensing). This sublicensing point may give rise to some tricky questions in some countries but, on my line of argument above, it would fall away as there’d be no need for a right to sub-license under the GPL.
Turning now to the real world of theme reviews, there is no legal requirement to take the broader approach to images in themes for the WordPress.org theme repository that I’ve sketched out above. It ultimately boils down to a policy call on the part of those who control the theme submission process for WordPress.org. If they wish to stipulate that all images must be provided under a GPL-compatible licence in terms of the test above (or be in the public domain), that’s their choice (even though people may scratch their heads about the suitability of the GPL for images). All I’m saying is that arguably they are not forced into that choice by the requirements of the GPL itself. There may be other options. Some of those options might provide greater latitude for theme authors and without creating a significant additional burden for theme reviewers.
Additional guidance would be needed in the Theme Review Handbook, so as to help theme authors go about things correctly and help theme reviewers with what they should be looking for, but that wouldn’t be too challenging. You’d probably have three paths for images: one path for images that are released, expressly, under the GPL in their own right (which would require some explanation as you don’t really distinguish between object code and source code when dealing with images); a second path for images released under CC0; and a third path for images released under CC-BY or CC-BY-SA (there are other Creative Commons licence variants but I don’t think any of the other ones are appropriate as they impose ‘NonCommercial’ and/or ‘NoDerivatives’ restrictions). Each path should, I suggest, cover the issue of model and property releases in relation to images that show identifiable individuals or copyright protected property.
I hope this post answer’s Ulrich’s questions in sufficient detail. If not, feel free to shout. Turning to the GPL/CC-BY and CC-BY-SA compatibility point (in relation to images), it would be great to know what the community thinks about my suggested approach. And if any lawyers out there are reading this, please feel free to chime in. The more the merrier. I don’t expect everyone to agree with me. After all, discussing these sorts of GPL questions can be a bit like slipping into a cosmic black hole.
(The photo I’ve used for this post’s featured image is by Milada Vigerova, released on Unsplash under CC0. Because it has been released under CC0, I have no obligation to credit the photographer. However, credit where credit is due I say. Thanks Milada! I don’t know whether a model release was obtained. If the subject of the photo asked me to take it down, I’d do so immediately.)