Sometime back I came across few stories suggesting Google displaying AdSense ads in their popular image search results. Many bloggers captured screenshots of AdSense ads being served in Google Image search results last year. Even I saw AdSense ads sometimes back but today almost every image search I made displayed AdSense ads.
Another thing I have noticed for most of the queries ads are being displayed on page 1 of image search result only. Also ads are shown only at the top (may be considering width of my widescreen monitor! :P)
Anyway below are some screenshots of Google image Search for some top queries. It looks like AdSense for Image search results have less takers as only one ad slot out of three/four is filled most of the time.