The first question anyone would likely ask in regards to this is, "why would you want to advertise on Google Image Search in the first place?".
It all turns on the idea of 'Associate Name' - a term which refers to a striking marketing image or branding logo associated with a company or a product. If you were able to bid on a brand image or company logo that you could associate with a keyterm - via Google Image Search - you would have access to a very powerful marketing tool.
Of course, any images of adult or inappropriate content which are linked to your keyterm have already been taken care of by Moderate SafeSearch. But if it was possible to stretch this idea to bidding on terms like 'Holiday Resort in Spain,' and then placing an image of your villa at the top right corner of the page, how much more effective would advertising be?
The existing Google Image Search already has advertising-friendly relevance constraints in place with another Google product, Google News. If you search for an image that happens to be topical, then the results shown will deliver images from Google News to the top of the Google Images results page; is this not a form of advertising?
It should be pointed out that this is not merely a placing of Google AdWords on the Google Image Search results page; it's an introduction of a solely image-based version of AdWords onto the search results for images. Are Google merely waiting until they have enough of an image store before they roll it out? Should features such as the Google Image Labeller be seen as an attempt to do this?
Time will, no doubt, tell.
