Witches are known to like to disguise themselves. The Chief Witch always liked to look uglier than she actually was as she had no time for vanity and liked to be different from the norm. Where the stepmother in Snow White disguised herself as a crone, the Chief Witch saw the crone as being useful place to start from.
Despite that, each magical being has a unique code they are born with and which cannot be changed. Magical codes can be read (and therefore people identified) with the aid of a wand or a crystal ball. The sprite communities moan about this as they don't use wands or crystal balls. The rest of the realm is not sympathetic. They've taken the chance to either use wands/crystal balls themselves or are on good terms with others who use them and see no reason why the sprites shouldn't do the same. Sprites are inherently lazy and the rest of the realm sees their vulnerability at not being able to read codes (and therefore take action to avoid those who threaten them) as the price they pay for that laziness.