I composed an Imgur album out of potential background images for the game, those specifically requested and more.
http://imgur.com/a/8Mn8DOf course, these are not formally mine, they're ripped backgrounds from various eroges and visual novels. I believe practically the amount of people who give a shit is as close to zero as possible, but I still feel like stating this is necessary.
I specifically uploaded only images that would have any potential use for Whoremaster (although there's a mixture of both modern and fantasy settings). I'd highly recommend one of the city-scapes for the Main Menu or New Game backgrounds. It's the one I've been using personally.