Does it have to be something that captures the screen activities in real time? By this, I mean you want it to be like Team Viewer? Or, would it be something that captures screenshots for a certain interval (e.g. every 3 minutes)?
If you are talking about the latter, then I would recommend Time Doctor. That is the employee monitoring software we use at work. Not only does it accurately track our work hours and computer activities, it increases our productivity by providing us with a detailed analytics of our workday.
Here is a video of how it works: http://www.youtube.com/watch?v=YoUPKvBJtDU