Here's an idea to prove they're watching the videos...at intervals, you display a unique ID to each feed, that the monitor has to enter on a keyboard. The interval should vary, as should the position on the screen. But the UID should appear on everyones feed at the same time; this should prevent one person from monitoring more than one feed at a time. You could/should have every feed monitored by more than one person. The feds could be run slightly out of sync/delayed, but still with the ID displayed at the same actual time. Therefor is someone was distracted by having to enter the ID, and missed someone shoplifting, another person wouldn't be.