One of the coolest features in Microsoft Office 2010 is the ability to blur pictures and remove backgrounds. I recently had several screenshots for a manual where the background was solid black. With one click I was able to remove the black backgrounds and reduce the amount of toner used for printing. If you're not using Microsoft Office 2010 there's always Photoshop and other third party software.
To learn about these features with a step-by-step guide take a look at the article "How to blur the background of a picture in PowerPoint 2010" from TechRepublic, on of my favourite publications. These picture editing tools apply to all of Office 2010, not just PowerPoint.