thank you for the fast answer
the first link was very helpful
but is there something that more like this: http://www1.istockphoto.com/file_thumbview_approve/1063191/2/istockphoto_1063191_real_scrambled_image_on_tv.jpg or http://1.bp.blogspot.com/_z5T4oKOg5oQ/SY13SYtAAvI/AAAAAAAAAC0/qvDNkgoG4fw/s400/plasma-screen-distortion-2.jpg ??
i tried to find a overlay, but apparently there is nobody who makes pics of videocam/tv noise (why)
thx