Matt Cutts of Google tweeted that Google added a special feature to image search based on Lawrence Lessig's request. The thing is, the feature has been available since 2009, Google just moved it up in a more prominent area.
Now, when you search in Google Image search, part of the "search tools" are the usage rights. Here is a picture:
It is nice to have up in front but you can't always trust these filters, the usage rights may be wrong, changed or the site the image Google indexed may have stolen it. So be careful using this feature.
Forum discussion at Twitter.