indyank - 3:57 am on Jun 12, 2012 (gmt 0)
My suggestion would be to focus on user comments/reviews rather than adding more words to describe the picture. Picture is said to convey a lot of words and why should one waste time on adding additional textual description beyond what is needed? Is it for google? If the answer is Yes, then don't do it. Because, you are essentially converting a page that might be falling within Google's "shallow" definition into some thing that might be genuinely (i.e. not falling within google's definition) duplicate or redundant.
But user comments/reviews are more natural and an active discussion would definitely convey the interest/popularity to users. Yes, this can be and is already being manipulated. But if you are worried about google, I do see them ignoring these as they probably can't find out whether they are genuine third party comments or "paid" comments.
Thus, if you have art/picture sites, the best thing IMHO is to have UGC.
ps: A few days later they might come up with some technology to understand the words behind the picture and then they might penalize you for having duplicate content on the same page. :(