I think there's a good chance some service will integrate this in the future, and it would be amazing.
I already use Google Image Search for this. I search by image, using the photo button to upload one of my family's unidentified 1800s cabinet cards. If that photo appears anywhere else on the Web that Google has searched, it will show me. I haven't had any luck yet, but maybe as more and more people scan and upload their photos, someday there will be a match.