Source: http://feeds.gawker.com/~r/lifehacker/full/~3/K1TQiPz2vYc/google-images-adds-similar-search-function
From a cursory few searches, Google's own similar image search seems to perform a bit more accurately when it comes to hunting down real-life images that look like other captured images. You can't upload or draw your image basis, as with GazoPa, but then you get greater results filtering with Google as well—exact dimensions, color saturation, file type, and more.
Both sites are worth keeping bookmarked if you're often digging around for something just a little different than what you're working with.
