@Richi007: Let's put it that way: If you interpret all bytes of your picture as one big number, then finding the number is a task with an equivalent effort to finding the bytes, which define the pixels, don't you agree? Finding the bytes/pixels is like faking it.

If you have such a database, you don't only have all pictures you want, but you also have all pictures you want with errors. You might find a picture that looks like the one you were searching for, but looks like a cheap photoshop fake. The real looking one is only one of incredibly many.