Exactly. If your system monitors a place like a halfway decent railway station half a million people per day is a number you could expect. Even with an amazingl

Exactly. If your system monitors a place like a halfway decent railway station half a million people per day is a number you could expect. Even with an amazingly low error rate of 1% that would result in 5000 wrong signals a day. If we make the assumption that the people are uniformly spread out througout a 24 hour cycle that means a false alarm every 20 seconds. In reality most of the people are there during the day (false alarm every 10 seconds) and the error percentages are nowhere near 1%. If you do the math to figure out the staff needed to react to those false alarms in any meaningful way you have to come to the conclusion that just putting people there instead of cameras would be a safer way to reach the goal.