I guess I should comment here, but I don't have much to add. Most of the questions that arise naturally about how this was done, and about primes in general, h

I guess I should comment here, but I don't have much to add. Most of the questions that arise naturally about how this was done, and about primes in general, have already been asked and answered. Still, given my username I should add something ... So if the size was prime x prime then the fact that the number of bits is a semi-prime tells you the size of the image, even if all you have is a stream of digits. Then the "noise" at the end will tell you what the least significant bits are, and hence you get an image without very much ambiguity. Just thought I'd mention that.