There’s a story in wired about licences in flickr photos. The problem is that flickr requires users to tag each photo with one of a range of licences (including “all rights reserved”). Users can change the licence at will, either on individual photos or on thousands at once.
If a third party takes a creative commons licensed image, reuses it under the terms of the licence and the user subsequently changes the licence on the image on the flickr site, difficulties arise.
The creative commons licences are perpetual, containing words like:
“Subject to the terms and conditions of this License, Licensor hereby grants You a worldwide, royalty-free, non-exclusive, perpetual (for the duration of the applicable copyright) license to exercise the rights in the Work as stated below:“
So the third party can continue using the image under the creative commons licence indefinitely, provided they have a local copy. The user (the copyright owner) has now removed their offer of the image under the licence, so proving they are entitled to use the image could be problematic, unless they’ve done their homework and kept some form of log of the licence. Getting a new copy of the image under the old licence if they haven’t kept a copy is likely to be impossible.
I have no idea what happens in the case where an image is pulled dynamically from flickr and built into a composite in a way which breaches the new licence. Presumably such dynamic system need to check the licence every time, as is entirely possible using the flickr API.
The take home message? Keep track of what software and content you’re reusing, keep and archive a local copy of everything you use.