TheOneSpy (TOS) has a feature called camera bug in which you can take snapshots from a computer webcam after a predetermined period. Thus a log can be generated, and a person or a subject is observed for presence.
You can create and send multiple bugs on TOS. The bug is nothing but a small, configurable command that is generated by a few simple clicks. The command tells the computer webcam to take snaps after predetermined intervals, and you can create multiple cam bugs and generate a log that can help you assess of how much a worker has worked or how much hours your kid has used the computer.