I was once involved in a project which projected Aruco markers in IR. So you get a slide projector, swap the bulb for an LED, have some slides made at the photo

I was once involved in a project which projected Aruco markers in IR. So you get a slide projector, swap the bulb for an LED, have some slides made at the photo place, and you're done, right? No - slide projector slides are IR transparent on purpose, so that they don't absorb heat from the bulb.