Foap released a few years ago, as app that allowed it users to sell photos. Since its initial launch it has blew up in popularity and continues to grow on a daily bases. You can sell your photos how many ever times you want, by selling it all your doing is giving them rights to use it, they might use it in a commercial, ad, or even there social media profile picture. You can only sell photos for $5, no more no less.
My experience with Foap
I uploaded a few images to foap and absolutely loved the site, its easy to navigate, its got a great user interface. Oh yes and i forgot to tell you its available on IOS or android, its cash out options are PayPal. They generally pay you imediatly after the transaction. If your photographer this is the app for you, and who knows if you can get enough popularity you might be able to make a real income off this