Re: Card Number?
You're right, but you can't.
NDS decryption is only available on Sky hardware and some professional IRD's.
Even Virgin Media customers have a UUID displayed on the screen in-vision during the viewing of sports content from Sky. I'm sure BT Vision will have similar piracy prevention too.
Coming soon; digital watermarking, which can't be obfuscated by simply covering the numbers and is easily detected by automated harvesting.