Scenario A: A picture is directly inserted into PPT, cut and spread all over the screen to get a PPT background; However, the right-click menu has no option to save the background.

Scene b: click PPT to set the background format, and select "picture or texture filling" as the filling method-insert a picture from "file" or "clipboard", and select the same picture as scene a to form the background; The right-click menu has the option of "Save Background".

There seems to be no difference between the backgrounds formed by Scene A and Scene B, but the background formed by Scene B has the option of "Save Background" in the right-click menu, while Scene A does not. Therefore, the background formed by scene B is the real background and can be saved as the background; The background of Scene A is not a real background, but a big picture.