At first glance, oDesk, a site that helps employers hire, manage, and pay online contractors, looked like just another marketplace to Web developer Jason Cartwright. So when a former colleague booked him to work on a few projects already managed through oDesk, Cartwright agreed.

There turned out to be one catch: oDesk’s electronic monitoring feature, which takes computer screen shots randomly six times an hour. If you’re reading personal e-mails or watching YouTube on billed time, your employer will find out. ”As I’m an independent developer, it was very invasive at first,” Cartwright says. But he quickly got used to the screen shots and saw the flip side. ”I like the accountability. Knowing that I was being monitored forced me to reduce distractions and stay focused.”

He’s not alone in not seeming to mind. Some 100 000 Web developers, programmers, graphic designers, writers, and other contractors, most of them working outside the United States, have put their profiles on oDesk since the company was launched in Menlo Park, Calif., in 2004. But not everyone thinks the electronic monitoring is ethical. Critics have called the feature ”Big Brotherism” and even a form of slavery.

But all work requires accountability. When output is hard to measure, you pay by input, which is why lawyers, French tutors, and physical therapists charge by the hour. When output is measurable, you pay by the job, so writers bill by the published word and house painters by the square foot. The point of oDesk is to make both options available.

Gary Swart, the CEO of oDesk, argues that when small businesses hire independent contractors for quick-turnaround projects, his service can benefit both parties. Employers know that their work is getting done and that they are not being overcharged, and contractors rest assured that they’ll be paid for their time and effort.

Swart says that oDesk tries to make remote work and outsourcing more effective by emulating the real world. Contractors log into a ”team room,” which punches them in on an Internet ”time clock.” oDesk then tracks the time and bills for it, taking care of currency conversions and international payments.