I don't think that is possible, how can it recognize those black bars? I think it is easiest just to make people cut the black bars away, before they upload a picture, it looks better in any way I believe :)!
It's not much work (especially if you compare it to the time you already spent taking the shot) and to do it automatically will only cause problems with some shots:
I think if a picture has really small black bars up and down, it sometimes looks better if you don't cut them, for example http://whatthemovie.com/shot/34889 like this you get a nice frame around it, which looks much better than only black bars on the left and right. But if the bars are bigger they should just be cut off course.