Slow shutter speed would be my guess If it was a camera only photo. Or that could also be done in Photoshop.
e.rose said:A slow shutter speed would give you blur... not multiple instances of a person in the image.
They took several different frames, layered them in Photoshop and then lowered the opacity of each until the bottom layer (of them kissing) was revealed to their liking.
You have to put the camera on a tripod for something like this. And then you have not NOT MOVE IT AT ALL... or the background won't line up in each layer.