Which tag, out of glasses_removed and no_glasses, should be used when the character's glasses are still present in the image, but being worn by someone else? The current wiki entries are not entirely clear on this. glasses_switch covers this situation, but it really needs to be used in tandem with one of the other tags (right now it's inconsistent which of the two is used, if at all) to make it easier to search images where two pairs of glasses are actually being switched.
Whatever is decided with glasses also needs to be consistently applied to other objects that may be removed and worn by other characters, such as headwear and eyepatches.