Feature summary (what you would like to be able to do and where):
User cropped a CC BY-SA photo from Commons, correctly stating that the new image contained a work from another media and correctly indicating that the original photo was under a free license. What happened is that there is no longer a correct space to say what the source was. Such space, such as a "source" field, should be reinstated/created.

Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
All cases in which a crop of an existing image is performed, and more generally all cases in which an allowed derivative work is created.

Benefits (why should this be implemented?):
It would allow users to correctly comply to Creative Commons licenses and to Commons guidelines.