You can change the transparency of a picture used as a slide’s background with the

The answer is Format Background.

Format Background is a feature of Microsoft Office Professional Application to change the transparency of a picture used as a slide's background. In this feature, you can also change the stretch options of the background image, fill settings, brightness, and contrast. In 2007 version of Powerpoint, it is found under Design Tab > Background > Background Styles.

(on android mobile) click on "me" and then on your profile picture

Kpa - known-plaintext attack