Masking parts of an LCD with software

Hi everyone.

I have a 7" LCD which has a VGA and a RCA input.

It's going to go to in my car eventually. The RCA input will be connected to a reverse camera. I need to make something up to go between the RCA input and the reverse camera to mask (in black) parts of this input. So when you get a square picture of whatever's behind your car, I need some of it to be masked in black.

Is there a device or way of doing this at all?


There is a video experimenter shield which enables you to overwrite part of a video stream. You may need to convert the video stream to a format supported by the shield, but it seems like the sort of thing you're after.