How did you find the photos with this smear effect? Is it made by computer or the function of camera?

You can shoot it with the camera itself ... it's not the function of the camera or anything, it should be regarded as a photography skill.

The specific operation is like this. First, there should be some lights in the environment, but not too strong. Then the camera turns on the flash to synchronize with Hou Lian, and shoots with a low-speed shutter.

Because it is a low-speed shutter and the subject is constantly moving, the part with strong reflected light will be exposed in the camera, forming a smear. Of course, the exposure time of the shutter should be controlled well, and these smears should not be overexposed. Then, turn on the camera synchronized with Hou Lian. When the shutter is about to close, the flash will be activated, and then under the irradiation of the flash, the shape of the person will be fixed on the film or photosensitive element.

This shooting method is also to shoot cars with trailers, and the principle is basically the same.

Of course, to use this shooting method smoothly, you need to have higher requirements for flash control, shutter speed control and metering.

Of course, you can also create a new layer and drag it to an inappropriate place later, but it takes a lot of skill to make such an effect.