I don't think that the concept is workable. I can't get the file size down to the point of practicality unless I go with basically a grayscale pallet. The photo's get grainy with higher compressions but that isn't a show stopper. I have seen some stuff that is released by the two political camps that seems to favor the throwback style- like a black and white commercial from the sixties almost.
Just something I was tinkering with and thought I would share. Feel free to comment, feel free to share any suggestions for reducing the file size as well. The size of the signature shown above is 400x100 pixels. Color Pallet used is 31 colors.