A bit of a Catch-22 (Joseph Heller I think it was just to attribute) situation I find myself in. I would have preferred to comment but do not have enough credibility yet so will answer instead and risk my meagre credibility, I hope the answer summarises the thoughts in the above comments in part.
Looking at Wikipedia entry for fair use
we can see that attribution is not directly related to fair use (search the article for 'Acknowledgment of the source makes a use fair').
Having a field that people can put in an attribution would be handy and would increase compliance with attribution.
Having a text box that pops up with information about fair use before you can check the tick box that says you believe the use of the image is fair or permission has been given by the copyright owner would solve that problem to a large degree.
It also seems that the global copyright landscape is not flat and never will be though fair use or similar relaxations exist in many countries for EDUCATIONAL purposes. With this in mind it might be 'safeish' to assume that much use of images on SE will be covered and perhaps a fair use undertaking check box is not needed and attribution could be added if it was easy to implement rather than as a requirement for legal need.
Personally I think the attribution feature would be nice to investigate associated images for more information about the question if it was copied from the web, sometimes a novice will neglect to link the pertinent data-sheet page and require more questions before a solution can be found.