Some sources of images with an open license.

[Chronon]

That's a good question, soap.  I also wonder about derivative works.  I have assumed that an image having no copyright means that people can modify the image.  Does the person who modifies a public domain image get to hold a copyright over the modified image?  Here's one perspective on it:

2. Public Domain Works That are Modified

Modifications to a public domain work may be protected by copyright and cannot be used without permission. A famous example used in many copyright classes is of the artist who paints an elaborate hat and mustache on the Mona Lisa. Even though anyone is free to copy the Mona Lisa image, the modified image (with mustache and hat) is protected under the artist 's copyright.

I see that a lot of CC licensed images also require attribution.  So, themes should have some way of describing which images are licensed, under what terms and by whom the copyright (if any) is owned.  Should this be a 'guideline' that we clearly state in ThemeGuidelines?  There was no mention of licensing issues there at all until I made the change yesterday.

[ZincAlloy]

CC licensed demand attribution "in a manner specified by the author".  Nobody really specifies a way in which he or she should be credited. Can it be assumed that the username /real name (where specified) is the actual specification for attribution?
As CC licenses are designed to make the use of  creative works possible without having to ask for permission, not specifying the right approach for attribution seems to defy the purpose of the license..

[Llorean]

@soap, Chronon: I more or less agree with Chronon's quote there. As far as what I've ever read covers, for items that are in the public domain derivative works may be relicensed at the author's pleasure. Public Domain is not sticky like many licenses, so any original work added by you is still copyright you, and so the whole work falls under your restrictions since PD doesn't offer any restrictions (including to what restrictions you can put on your changes).

@ZincAlloy: Unfortunately you can't really "assume" anything about Copyright. It all has to be explicit. If they say "you can't redistribute this without attributing me in the manner of my choosing" then refuse to tell you how, that's actually an explicit statement saying "you can't redistribute this" because they've (unintentionally) refused to take the step that gives you permission. I know this is problematic, but maybe it's time to start educating the creators of materials that you want to use what *their* obligations are in order for the license to work? I'm sure if they knew they just had to post a statement somewhere describing what attribution was necessary for their CC licensed works they would, and being educated on it would prevent issue in the future.

[ZincAlloy]

too bad...
creativecommons.org doesn't warn the users about this when they choose their license... odd, really.

[Chronon]

I did ask about this in the #cc channel on Freenode.  I only got a response from one person:

<nkinkade> Chronon: The general way to attribute will be to 1) Cite the author's name 2) Give a link to the original work 3) Give a link to the CC license.  If the author hasn't specified anything particular about the method of attribution, then that should be adequate.

I tried to read the actual text of the license.  I think section 4(b) is the relevant section.  Unfortunately, I am no lawyer, so I cannot offer anything but unprofessional opinions. 

If You Distribute, or Publicly Perform the Work or any Adaptations or Collections, You must, unless a request has been made pursuant to Section 4(a), keep intact all copyright notices for the Work and provide, reasonable to the medium or means You are utilizing: (i) the name of the Original Author (or pseudonym, if applicable) if supplied, and/or if the Original Author and/or Licensor designate another party or parties (e.g., a sponsor institute, publishing entity, journal) for attribution ("Attribution Parties") in Licensor's copyright notice, terms of service or by other reasonable means, the name of such party or parties; (ii) the title of the Work if supplied; (iii) to the extent reasonably practicable, the URI, if any, that Licensor specifies to be associated with the Work, unless such URI does not refer to the copyright notice or licensing information for the Work; and (iv) , consistent with Section 3(b), in the case of an Adaptation, a credit identifying the use of the Work in the Adaptation (e.g., "French translation of the Work by Original Author," or "Screenplay based on original Work by Original Author"). The credit required by this Section 4 (b) may be implemented in any reasonable manner; provided, however, that in the case of a Adaptation or Collection, at a minimum such credit will appear, if a credit for all contributing authors of the Adaptation or Collection appears, then as part of these credits and in a manner at least as prominent as the credits for the other contributing authors. For the avoidance of doubt, You may only use the credit required by this Section for the purpose of attribution in the manner set out above and, by exercising Your rights under this License, You may not implicitly or explicitly assert or imply any connection with, sponsorship or endorsement by the Original Author, Licensor and/or Attribution Parties, as appropriate, of You or Your use of the Work, without the separate, express prior written permission of the Original Author, Licensor and/or Attribution Parties.

So, it appears that there are default conditions written into the license.  I don't think we need to avoid materials just because the author has not given specifics about method of attribution.  But it would be nice to have the opinions of someone in this field.

[ZincAlloy]

great. this is making things a lot clearer and easier.. I'll put up my new theme later today..

[Llorean]

If the license itself sets default conditions, that's fine then, yes.