dimensions do matter though. make a two colored .png that is 100000 x 100000 big… even if it’s just 10kb or something, older computers will shit bricks. that is because images always end up decompressed in memory.
though I doubt it actually matters when talking about 500 x 500 and just one image, it’s just something that can’t hurt to keep in mind.
oh, and if you’re using .png, you want this btw ;)