Gaming website 3DS Buzz claims to have a real picture of a working 3DS, which based on comparison with the official 3DS images released by Nintendo, appears to be real.
The leaked pictures apparently come from a worker in one of Nintendo's factories. The picture shows the black version of the portable console that comes with a white thumbstick. There is even a leaked video showing the 3DS in action, which you can view here (note: these videos have been removed rather quickly, so the link may not work anymore).
The 3DS is scheduled to be released in Japan on February 26, and released in other markets starting in March.
Here's the leaked picture in question:
(Credit: 3DS Buzz)