But it only works well if the crowds move out of the way reasonably quickly. If we're taking about areas packed with people all blocking a certain area, and you need hours of shots, the change in ambient lighting over time will have negative effects on the end photo.
There's an analogue method too - just do a very long exposure of a busy street. There is so little reflected light from people (relatively speaking) that it barely registers on the film/sensor, hence they are 'invisible' in the final shot. That's why old street photos are sometimes empty of people, because both lenses and film were slow, leading to long exposures.
https://digital-photography-school.com/taking-photos-in-busy...
https://petapixel.com/2019/09/18/how-to-shoot-people-free-ph...
But it only works well if the crowds move out of the way reasonably quickly. If we're taking about areas packed with people all blocking a certain area, and you need hours of shots, the change in ambient lighting over time will have negative effects on the end photo.