The core assumption here that the color depth is fixed or that the frame size cannot grow is flawed. We can always increase both, creating infinite possibilities.

Also you'd have to generate these images for them to exist and not merely be probability.

The logic applies for any given resolution or color set, I'm just using full hd here because is the most common (same for color) and enough to display a pretty detailed picture, the core idea here is that no matter what kind of image you are trying to make, it is already constrained into a finite set of combinations.