Hey:
I DSP or other 32 bit computer is best for image processing. But a lot depends on what you are trying to do. I have seen 8 MHz Z80's used to do some image analysis. All depends what you are trying to do and at what cost.

If there is no concern how long it takes to process a captured frame then an 20MHz or 30MHz processor with 4x or 1x clocking might do a right nice job. Even a 12 MHz processor with 12x clocking can do some jobs.

Heck....A friend of mine is setting out to build a Video Motion Detection system using a PIC processor using a B/W NTSC camera and his design probably will not even have a frame grab function in the conventional sense. (I am waiting to see how he comes out on it).

Michael Karas