There is no particular genre, it is a personal hobby of individual painters. There have been such painters since the Renaissance, and this phenomenon can be seen in 17, 18, 19 and even in western paintings in the 20th century.

In the painting "The Envoy" by holbein hans Jr, a German Renaissance painter, there is a skeleton hidden in an obvious place, but it is subtly distorted, so it can only be seen from the oblique bottom of the painting.

http://www . wga . Hu/art/h/holbein/Hans _ y/ 1535 a/ 1 ambassa . jpg

/kloc-Italian painters Algin bordo and Azeem Baud in the 6th century like to create portraits with flowers and fruits, http://www.wga.hu/art/a/arcimbol/seasons8.jpg..

He left many such works: http://www.wga.hu/html/a/arcimbol/index.html.

It can be seen that this kind of painting had a good commercial interest in Italy at that time.

Modern surrealist painter Dali also likes to do this kind of visual magic, such as http://dali.urvas.lt/forviewing/pic06.jpg in The Bust of Voltaire Disappeared in the Slave Market.

There is no internal connection between these people. The definition of painting school is a group of painters who live in similar areas in the same period, have similar artistic ideas and aesthetic pursuits, consciously or unconsciously. So in any case, it can't be said that this is a painting school.

There is a simple reason. The original painting technique of creating three-dimensional space on two-dimensional canvas is a kind of visual deception, a further deception on the basis of deception, and a philosophical game played by artists. In fact, painters in ancient China also played this game. The Journey to the West in Fan Kuan is an example. It can be said that it is extremely difficult for contemporary appraisers to find the artist's signature from rocks and trees.