I’m not going to claim to understand the process by which French duo Lucie & Simon captured these images of cities like Paris, Bejing, and New York without people (save for a single figure). It involves using a “neutral density filter that allows for extra-long exposures, which removes moving objects like people and cars.” How that works or what a “neutral density filter” is, I really cannot say, however, the images produced speak for themselves (and are of much higher resolution on their site.)
I lived in New York for a short time, years ago, and the effect of seeing it this empty is really stunning. The only time it ever came close to this when I was there was early in the morning, on my walk to work at 5:30 or so, and even then, it depended on the neighborhood I was walking through at the time and there were always a few cars. It’s eerie to see it looking so quiet.