Removing tourists from photographs

It isn't unusual for a site one would like to take a photograph of to be constantly full of people (eg: tourists) milling around. The likelihood of getting a photograph with no one in the shot is slim.

One option is to record a video and then average the frames together. The video obviously needs to be capturing from an absolutely still position, for example, on a tripod. The averaging of the frames will have no bearing on the static structures but moving objects will become less bright as they get averaged with the static structures. The following is a 1 second (30 frames) average around the time of the image above.

The longer the averaging the more effectively moving people will be removed. And finally, a 4 minute average over all the frames in the video is presented below. The technique relies on movement, so the people on the front pews remain visible since they didn't move. The slight blur in the center towards the front is the result of someone standing for some time taking photographs of the building.

One can also take a rolling average, this is a 1 second sliding window and titled "chem trails".