Click the right mouse button in the blank space of the slide and select Set Background Format in the pop-up dialog box.
In the right column, select the picture or artistic fill in the fill, and then click File.
Select the PPT picture to be filled in the pop-up dialog box, and click OK.
The above is that concrete step of setting PPT picture as background picture.
Second, how to set PPT pictures to all the same pictures?
This is simpler. After all the steps in the above tutorial are set once, click the Apply All button below to set the background of all slides as the same picture. I won't explain it in detail here, because I have to explain another method: applying master style to unify PPT background.
Open the folder where the PPT background picture is located, and open the PPT software.
Locate the view on the tab, then click the slide master and select the large slide thumbnail on the left.
Drag the picture onto the PPT slide.
Exit slide master