You got undeveloped film from somewhere? Nice! Go and develop it in the AV room. There's the photo development tray.
This is the low-spoiler guide for "Developing a film" puzzle in The Darkside Detective - A Fumble in the Dark. Unlike in normal walkthrough, you get gradual hints on how to solve the puzzle. Click the big button below to see your first hint. If the hint contains a spoiler, you will be warned about it before clicking.