In this photo illustration, an Instagram photo of various Facebook logos are seen on an Apple iPhone on April 9, 2012 in New York City. - 

A forecaster has dramatically hiked estimates for the money-making power of Facebook's mobile app -- suggesting $1.2 billion in mobile ad revenue by 2014. A criticism of Facebook all along has been the idea that while they can bring in impressive numbers of users, that doesn't necessarily translate to revenue.

And yet at the same time, Facebook is under fire today from some users for a change in the fine print of its photo sharing service, Instagram.

The new Facebook ad revenue estimates are from a data-crunching company called eMarketer.

"For many years, Facebook's revenue came from ad products that were really designed for the desktop user," eMarketer vice president Clark Fredrickson says. "Facebook developed an ad product that was seamless across devices."

That's dramatically increased the number of ads it has delivered on its mobile platform -- and with that comes revenue streams, according to eMarketer.

Follow Jeff Horwich at @jeffhorwich