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.
http://www.eileencarpenter.net/blog/worpdress-building-a-jquery-slideshow-without-a-plugin