I have tried the 'Image Credit' plugin but it seems flaky (possibly due to interaction with other plugins). What are other people using? The requirement is for each image used to have an associated field for copyright info.
You could use the description or caption part of the image editor/uploader and then query that for each image. To clarify what I mean read my the post I wrote at my blog for creating a sideshow in wordpress with titles and captions without using a plugin. I don't know if you're making a slideshow, but if you're not, take out the jquery part and it's essentially the same idea.