The Creative Commons license has different attributes, one of which is “Non-Commercial”. It simply states “You may not use this work for commercial purposes.” The literal reading makes it very clear you cannot profit directly from the work, such as selling it as part of an image library. But what if you are using it on a website that makes money from advertising? What if you use an image for your company’s website, where it serves as marketing and promotional material, indirectly resulting in revenues? Is that use commercial enough to invalidate the use of such Creative Commons content?
Philip Lenssen explored this question last year and got an inconclusive answer:
I’ve asked the Wikipedia mailing list a while ago, and recently received another confirmation from Creative Commons’ Lawrence Lessig: yes, the CC organization believes this being OK is the best reading of the license. […] But it’s also a matter of how you display ads, Lawrence disclaims, saying that there could be certain advertising schemes that take it too far.
(It should be noted though that the Creative Commons organization does not determine whether a judge would agree with their interpretation, in case someone would get sued over using NC content on an ad-supported site.
As Philip notes, many blogs and even Google would be in trouble if you could not use CC images on ad-supported sites. Still it does seem like something to be more safe about now than sorry later.
Another problem I saw recently is that some people on Flickr repost photos (taken by others or professionals) under a Creative Commons license. They actually put a copyright notice stating they got it from AP or somebody, but the picture is under their account with a CC license. I suppose this happens according to their account settings, but it can be very misleading.
It is possible for people to change the copyright for their images from a CC license to a more restrictive CC license or basic copyright. It can be a pain to prove that you had used the image under the correct license. Image Stamper is one service that may be helpful in that. It records the license when you used it so that you can use that as evidence if you ever require it.
None of this should really matter for small-scale bloggers and non-commercial websites, because it is not profitable to sue them. But we have seen what the RIAA did in the music industry. And there is always a non-zero possibility of somebody creating problems.