Or you could conclude that this person is in there to just get stuff done, and couldn't be bothered with wasting their time to fill in their profile, or was concerned with how their data was used by Github, or is a woman, or is part of a minority group that couldn't possibly benefit from posting a photo, or... There's all sorts of reasons why people don't post their profile online, and factoring this into your hiring criteria is about as valid as using graphology.