An iPhone app as a document projector?

First of all I have to say that it was super difficult to even post my question since I had to pick a community, and when I found iOS apps it didn't let me choose that unless I picked some arbitrary, pre-designated sub-community that didn't meet my need at all.

I just wanted to ask if anyone knows of an app that uses the iPhone's camera as a live, real-time camera (like a webcam), sends that signal to a projector in order to project documents, like an Elmo. It would be great to mount my iOS device and project what I'm writing onto the board.