They take your picture and then you get a mostly automated letter with the picture saying you have to pay a fine, but mostly you can ignore them. I lived near an intersection with one, every time the left turn light turned red (which happened way faster than normal) the picture flash went off for the last three or so people going through the intersection, presumably all of them getting tickets. I assume they are also recording the license plate numbers of everyone going through the intersection regardless of perceived violations.