This will be made difficult by people in your friends list using photos of cartoon characters, possessions, family members, significant others etc. as their profile photos.
If they go further and use photos that people are tagged in, then it also has problems of people being tagged in photos they are not present in to get their attention.
For example, in my friends list only around 70% of people have photos of themselves as their profile picture. Boy/Girlfriends and babies are the next most common picture.
Even if you recognise the specific picture, it might not be helpful. For example, two of my friends are dating, and use the same picture with both of them in it for their Facebook profile pictures.
If they go further and use photos that people are tagged in, then it also has problems of people being tagged in photos they are not present in to get their attention.
For example, in my friends list only around 70% of people have photos of themselves as their profile picture. Boy/Girlfriends and babies are the next most common picture.
Even if you recognise the specific picture, it might not be helpful. For example, two of my friends are dating, and use the same picture with both of them in it for their Facebook profile pictures.