These cameras are live and operated by the New York City Department of Transportation. You can see all of the cameras on a map at their website. (This site is not affiliated to the DoT in any way.)
Select a camera from the top to start. There are hundreds of cameras, but they might not all be working. If yours isn't, just try another one. The camera images update every second - wait a moment to see if it's working.
Part of a series which also includes Rorschmap and Street View.
Thanks to Ingrid Burrington for inspiration. Made in residence at Eyebeam.