If you create a 500x500 pixel image on your computer, you own the copyright on that image. But copyright isn't like patents or trademarks with "prior art": If I

If you create a 500x500 pixel image on your computer, you own the copyright on that image. But copyright isn't like patents or trademarks with "prior art": If I also make an image through some means (take a photograph, paint a picture, etc) that ends up being identical at 500x500 pixels, you don't own the copyright on my image.