blur behind moving objects

I use scenecapture2d to capture images.

Some moving people in the scene.

But the captured images show some blury shadows behind the moving people.

Why?? is it motion blur? I tried to turn off it, but nothing happens.

319116--20201018200031.png

Could it be AO?

what is AO?

Ambient Occlusion

no, it’s not, it more like motion blur

319213-12.png

like this