Whichever slide objects you place on your PowerPoint slide, their position and alignment matters a lot — be it shapes or even the many inserted pictures. In some cases, a haphazard arrangement of pictures may work — but most of the time you will have to align objects in a proper way on your slide. Even before you align pictures, you should explore whether all pictures are the same size or not.
Learn to align and distribute pictures in PowerPoint 2013 for Windows.

