Pixel-fitting by Dustin Curtis

The difference is subtle, but the comparison makes it very clear. There are several major problems with the computer-created icons that leaves them looking blurry and unimpressive. For example, in the transition from 66x40 to 48x30 pixels, the human version drops the border down to exactly 2 pixels but the computer drops it to 2.8 (that's two solid black pixels, plus one half-pixel at 80% intensity), which gives it an incorrect soft edge. The computer has no way of knowing that the border should always be sharp, so it ignorantly tries to maintain the ratio of the originally-specified image at the expense of sharpness. The result is not great.