For use on images that have borders on them, especially thin, solid-colored borders.
This tag is helpful since Bronibooru uses colored borders on image thumbnails to indicate various statuses (red for a post that's flagged for deletion, blue for a post waiting for moderator approval, black for a deleted post, etc.). If you add this tag to bordered images yourself then the mods will be very happy with you!
[BUY SOME APPLES]
(A more clever ad from the Ponygoons Ad System would be here if you had AdBlock off)