People in your social network may not post pictures, but for all the Facebook users I know, pictures is very critical part of their experience. [I personally don't use Facebook.] Facebook has actually solved the problem of sharing pictures with your loved ones for non technical people, IMHO.
Funny i don't use it myself, i get an email when someone sends me a message.
I know also people who share them, but max every week and probably just 5 friend really look at them. When you look at pictures, how can you concentrate on ads? They are not even in the middle like Youtube's. Pictures on mobile reduces the space for ads even further and you will always be uglier than every competitor.
I do not have any opinion about ads, I was only replying to your comment that no one shares pictures. Since Facebook, all the non technical folks I know have stopped using Flickr/Google Albums/Snapfish/Photobucket/<<Name Your favorite photo sharing Service>>. They also don't send pictures by email. They simply upload it to Facebook.
Ad serving (at least the monetizing part) isn't always about how you can make a user concentrate on an ad. How many free iOS games out there serve up unobtrusive ads that you sometimes even stop noticing?
