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.

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

Make images backgrounds transparent in PowerPoint to free up screen real estate.

Learn how to insert a watermark in Microsoft PowerPoint presentations. You can add a Draft text or an image watermark using the Slide Master.

To add alt text to images in PowerPoint, or edit an image's existing alt text, select the photo and choose "Edit Alt Text." ...

These files demonstrate the technique described in the article How to use create transparent text in PowerPoint 2016.