ODesk have time tracking software. This system makes screenshot every minute I guess.
It's very helps when you working with new developers. And you want to know for sure that he works on your project.
oDesk does one screenshot in each 10-minute period, at random. So you can be sure to have 6 screenshots per hour, but you can never know when the screenshots will be shot by oDesk software.
I've used oDesk as well and although I feel the feature is useful it also feels very invasive. Not knowing what it will capture (looking up something on SO, checking email, writing code) has caused me to have to delete a 10 minute time slice on multiple occasions just to avoid sharing a picture of my email index or similar.
Source: I work for an agency that does this.