Once you have understood the principles of empty space (that Garr Reynolds calls “negative space”), the rule of thirds, and other design principles of Powerpoint, you will discover that most photo backgrounds are too crowded. Those design rules are nevertheless fundamental to design effective sales presentations.
This is the reason why, for most images I use in PowerPoint, I extend the background and create more empty space for type.
This can be done thanks to graphic software like Photoshop. However it is very easy to do with Powerpoint.
How to do this with Powerpoint ?
1. Duplicate the image, and crop the second image… (ribbon / drawing tools / crop)
2. ….left and right, just to keep the background you want to extend
3. Extend the new piece of background
Up to you to select wisely parts of background that are quite neutral for a perfect result.
See this news in French: http://presentations-de-vente.com/comment-etendre-arriere-plan-photo-powerpoint