A bunch of unused images were removed from core in changeset 21498. Several of them were background gradients that were replaced with CSS 3 gradients. The rest have been unused in core for few releases.
However there are some plugins that use a few of these images and would need updating. Best thing to do would be to copy the images locally as that makes a plugin independent from core changes. If the images were gradients, best would be to use CSS 3 gradients (example).