In order to image the infrared light, we need an infrared camera. Fortunately CCDs in cheap consumer cameras are quite sensitive to IR, so sensitive in fact that it is necessary to filter out the ir in order to get good pictures. I got lucky and had an old intel web cam lying aroud in which the ir filter was a cinch to remove. Replace the ir filter with a visible light filter (so the camera doesn't see the projected display). I used the exposed end of a negative. See e.g., this
instructable for more details.