...when you find an image that looks *exactly* like the character in your WIP (not the main one but a major one).
I'd use this as a cover image if I could, but it wouldn't work for the novel as a whole. But for the character? Heck yeah. Even down to the earphones and gloves.
*clamps mouth shut as she doesn't want to give story spoilers away*
Edit: I love this image of the same model too: Second image