The right photograph can be a powerful communication tool in PPT slides. It can set the context of the presentation and help the audience process the content better. However, the picture should not distract attention from the rest of the content on the slide, reduce visibility or readability. To insert a photographs as backgrounds for a slide in PowerPoint 2007 and newer versions, right click on a blank part of the slide and go to Format Background>Fill>Picture or texture fill>Insert from>File and choose the required image file.
To adjust the brightness and contrast of the image to fade it, go to the Picture Corrections option in the Format Background menu and adjust accordingly.
If you’re using an older version of PowerPoint, right click on a blank part of the slide and choose Format Background>Fill Effects>Picture and click on Select Picture… to browse and choose the image file.