I sometimes insert copyrighted fictional character's images from a franchise on the rarest of error screens ("should never happen" type of thing). This time though, I work for a company, making their internal software, not as a hobby.
While no-one will probably ever see the fictional copyrighted character in question, and even if so, it's there jokingly and is not in any way related to operation of the professional software I'm making, does it fit under fair use? Is legality of this something that I should worry about?
Edit: What if the image in question is my own drawing of the character?