True digital signals are either on or off but they come in chunks. Your picture isn't solid chunk of info, it is put together with lots of packets of data. I have a feeling that a fast moving vehicle would have bits of data lost thus resulting in fragments of the screen being incorrect. If you have ever taken a Digital 8mm camcorder and hit the fast forward button or rewind button you'd know what I'm trying to get at. I'm not basing any of this on personal experience trying to do it, but to me it sounds like a problem you'd run into.