Scalado has a system that removes the people in the background of pictures:
“When capturing photos in a busy area, like a public square or a concert for example, it is often difficult to get a clean shot without unwanted objects entering the frame.
Now you can capture the shot anyway, and simply let the camera remove the people for you! Point your camera and take a photo. Afterwards you can remove anyone moving around, or select your friends and remove any strangers.”