There is another person's image in the photo taken. What's going on here?

Maybe you are talking about multiple exposures. Multiple exposure is a technical method in photography, which uses two or more independent exposures and then overlaps them to form a photo. Because the parameters of each exposure are different, the final photo will have a unique visual effect.

This means that this is a more creative way of shooting. Now many cameras and mobile phones will have this function. After taking a photo, you need to take one or more photos, and finally the camera or mobile phone will handle them. Some are automatically generated, some can manually adjust photos, and finally a photo will be generated. This photo will have the effect of overlapping several photos.