Nude (images that full display genitalia) and porn images of REAL people are not allowed in the character gallery.

Hentai or other artworks are also not allowed in the gallery.

Images with lots of skin, subtle nudity or other "Not safe for work" images can be allowed IF you change the thumbnail to warn people that there a NSFW image is inside.

Please keep in mind that these sorts of things can be VERY SUBJECTIVE. It safer to NOT use risque images for your character bios. If you are ever in doubt, you can send the picture to an Admin and ask.