2. Right-click any blank space in the PPT-Background editing area, and this will appear.

3. Click on the triangle in the above picture and choose the filling effect-click on the top "picture" to find out the picture of the main building you have prepared.

4. If you want to use the picture of the main building as the background of each slide, please click "Apply All" at the end.

I don't know if you understand, but we are alumni. The main building looks better at night, but the photos at night will be too dark.