Yes, I agree with you that the probability is there. But, even in the course of 4.5 billion years of this earth being in existence, that is not NEARLY enough time for even a basic painting to be purely imitated. It is, in fact, completely improbable. The more you throw the paint at the wall, you aren't more likely to get the image. However, the more you throw it, the closer you get to copying the image. For instance, if you throw a two-sided coin in the air a thousand times, the chances of landing a heads even once isn't 50%; the % gets closer and closer to 100%, in this case, at a rate of 50. There's a 25% chance that you will get the same side twice in a row, and so on and so forth.

With the painting example, even if you throw it quadrillions upon quadrillions of times, the chance is completely improbable and STILL only a tiny fraction of a percent, almost increasing at a logarithmic rate lol.