In PowerPoint 2007, you can remove the background from an image by using the Set Transparent Color tool. Here's how:
- Select the image by left-clicking it.
- Click on the Format menu.
- Choose the Recolor option.
- In the drop-down window at the bottom, click on the Set Transparent Color tool
- When your cursor changes, click the color on the image that you would like to set as transparent. This will remove the selected color from your image.
For more tips on using this tool, please see the screencast below: