You can search Google for pictures similar to a given image, for plagiarism detection or to find people that look like you.
Here's how I did a test:
Google returned pictures of people that look like me (see figure 2 and 4) - actually, pictures that look like the picture I uploaded, whether they represent a human being or not, or whether they represent a man or a woman. .
Figure 1: first picture of myself
Figure 2: pictures similar to picture in figure 1, according to Google
In this first test, the results reported by Google are based on metadata, despite my efforts to eliminate metadata in the picture in figure 1. Unfortunately, as you can see, the results are wrong. Google correctly figured out that figure 1 represents Vincent Granville, and indeed the first picture returned by Google is the one from figure 1. But Google displayed search results (images) related to Vincent Granville, as opposed to pictures similar to the one that I uploaded: that is, images associated with my blog posts on Data Science Central, or images corresponding to another guy who shares the same name Vincent Granville (and a friend of mine, incidentally).
Then I did a second test with the picture below. The results are a little more promising.
Figure 3: second picture of myself
Figure 4: pictures similar to picture in figure 3, according to Google
My daughter seemed to have been totally ignored by the Google algorithm, but at least Google's image search algorithm did not rely on metadata this time. My gender was properly identified in all but one image.
If you use an original image (not a screenshot), it has metadata (probably stored in the Google image index database) and Google will tell you which websites are displaying your image, based on the metadata. The screenshot tool alters the metadata, making image forensics (plagiarism detection) far more difficult, and could be used by pirates to upload copyrighted images and eluding infringement detection.
How to design a better algorithm? This is a computer vision problem, and this field has been very active for at least 30 years now.