You could lower those numbers significantly (humans can't discern 71381932 colours so why include them!, and 800 x 600 is too high a resolution - 400 x 300 would be acceptable.
It's fun to think of all the huge possibility of images that would appear. But remember: how could you find the image you want? Sure, you could have an index system - it'll be with the rest of the images somewhere, in all sorts of different fancy colours. There would also be endless lists of what images meant, but how would you know what picture was what? A minor constraint don't you think

As far as your maths goes, because we're dealing with images here I'm not sure but someone will no doubt confirm shortly: isn't it 800x600^(no of colours)? I admit I'm pretty bad at maths at the best of times so I am probably wrong!