That's what I've always wondered really, why are CCTV's often so bad? The old systems (from what I've seen on TV anyway) seemed to put the image of four cameras onto one video tape, reducing quality even more.

Of course, a million cameras running 24/7 produce an enormous amount of data, that just increases exponentially as quality improves. They can probably easily discard 90% of the footage with basic checks (is there anything besides the background visible), and use a smart compression algorithm, but still.