...they could help owners of copyright in images track down their "orphaned" works.
A hot news story in the UK in recent days has been the passing of a law to allow photographs to be published without the copyright owner's consent, provided a "diligent search" has been undertaken to find the owner. See http://www.bbc.co.uk/news/technology-22337406
Many photographers are careful to embed "metadata" within their photographs that explicitly declares the ownership of the image, but many online publishers (e.g. Facebook and the BBC) strip all such metadata from the "user generated content" they publish. This is probably excusable, since it's the only practical way to avoid the risk of obscene or libellous material being secreted in the metadata. By the way, if you're looking for an easy to use program to add metadata to your own photographs, I recommend Photini (what I wrote).
Apparently the new law makes it the photographer's responsibility to discover re-publication of his or her images and then to apply for payment from a central fund. The only problem is, how do you find out if one of your images has been re-published? I recently did a Google image search for my name, and found two instances of photographs I'd uploaded to Flickr being used without my permission. In one case the image was credited to me, in the other they'd included my name in their image file name. (In both cases, had they asked, I'd have said yes.)
With Google's huge database of Internet published images, and a bit of image processing software, they could make it much easier to find instances of an image being re-published elsewhere on the web where the perpetrator hasn't made it quite so easy to spot the theft. They already detect web pages with similar text, to reduce their pagerank on the assumption it's copied boilerplate text, so why not find very similar images in the same way? This would also help those performing a "diligent search" to find the true author of an image, rather than simply allowing them to assume it's an "orphan work".