This week's book giveaway is in the OCP forum. We're giving away four copies of OCP Java SE 8 Programmer II Exam Study Guide and have Kathy Sierra, Bert Bates, & Elizabeth Robson on-line! See this thread for details.
The easiest would be to install an application that can do so!
PlinkART, one of the winners in ADC-II, does employ image based search for finding works of Art(and if my memory is not failing me, the application was written by folks who were pursuing a PhD in the aforesaid field).
A couple of years ago, Google was doing something along the same lines; they were trying to build a repository of tagged images. Not sure if they made it public though.