I discovered something interesting recently. I knew that Facebook checked if it was a know connection before giving you access to your homepage and otherwise it tells you it is an unknown device. Well in my recent experience they made quite a lot of mistakes in the process.
I made a connection from abroad with my laptop so it was the same device but it triggered the same mechanism. To prove I was myself I had to identify people in pictures they uploaded.
The interesting thing is that some of the people I know have put family pictures up. One series of photos was the dad in one picture, the mom in another one and a daughter in the last one. Looking at the names I could figure out which name I had to select but it was interesting that it was 3 times a different person.
While doing the procedure I thought of how I would attack it and it would be actually quite easy. You just have to do some homework like figuring out family and friends which is not that hard. I guess facial recognition software would be a possibility too.