Could it be possible that high Google image traffic is related to good ratings after enabling "enhanced image search" from google sitemaps? I had always believed the results would be to help index pages and rank their quality directly, but surely it would make sense to use this data for ordering the google images results? How many of you having good traffic, also have "enhanced image search" switched on? Would your image descriptions that do well with the human testing done in "enhanced image search"? If you do have it turned on, do you ever play the "enhanced image search" game by rating other images? It would make it nice and friendly if participating made your site's images more likely to be rated by others.