What is the name of the photography technique that takes a photo and then puts it behind the object and takes it again to form a dislocation effect?

It should be called the combination of photos and objects. Remember the "Zhou Tiger" incident? It is said that the man put the picture tiger in the wild scene and then took photos to synthesize the photos of the South China tiger found in the forest.

In fact, if there is an electronic version of the child's photo, then take a photo of Apple with a digital camera, cut it out with a photo editing software such as SHOTOSHOP on the computer, and combine it with the child's photo (which requires re-composition, transformation and background processing), and the effect will be better than the previous processing method.