This kind of technology has been in the pipeline for a while but this is the first time I’ve seen it publicly available – and it’s awesome; being able to search for pictures that look similar.
(As far as I know this works in Chrome only, for the time being.)
So; do a google image search for a dress, jacket, pair of shoes etc. When the results come up hover your mouse over something you like, then drag the slightly larger thumbnail that pops up into the search box. You’ll then get results for similar images.