To make an image transparent in PowerPoint, you have to change the opacity of the image - and you can do it for the whole image or a part.

How Do I Create an Overlay in PowerPoint?. Employing the same design techniques that web developers use, you can make transparent and translucent shapes appear on top of other objects in your ...

You can make a picture transparent in your PowerPoint slides so that you can add text over it or use it as a background.