Google image search has now started showing Sponsored links at the top of the results page. This is still in the testing phase and these results are currently being shown only to a few users when they are signed in to their Google Accounts.
In 2007, Google had announced that they were losing out on as much as $200 million per year because they were not monetizing their Image Search pages. Today, though, a line of three “Sponsored Links” is showing.
Why Google hasn’t done this earlier is a question worth asking.