The [[Fan service]] article on en:WP has for some time included an image advertising "Kogaru Diaries", a graphical work that features depictions of child sexual abuse (erotic spanking of prepubescent girls).
The work is not notable; nor is its creator, beyond the fact that he is banned from Wikipedia (by ArbCom) and Commons, and allegedly also from DeviantArts.
While we encourage the creation of original artwork, using free artwork to advertise non-notable -- and in this case likely illegal -- off-site content in Wikipedia seems a bit off. Is there anything in policy about this?
Incidentally, the fan service article also features Wikipe-tan in a bikini to illustrate the fan service concept. Use of both images is being discussed on the fan service talk page.