If the size of the picture inserted in PPT is suitable for the size of PPT, you right-click on the picture, select Set Picture Format, click the size label, check the box in front of the best proportion of slide show, and select the size of the picture in the following resolution. Of course, the picture itself should be 640*480, or 1024*768 and other standard resolutions. If the resolution of the picture is 640*480, this item should also choose 640*480. And so on.