Often, the colors of images do not fit the color scheme of a presentation. One solution to this is to "take out the colors" of the image and replace it with a monochrome overlay with the most important color of your color scheme. As an example I have added some nice blue to my title page picture. How to do it (PowerPoint 2007):
Select the image
Click the "format" menu in the top menu bar
In the "adjust" ribbon, pick the "recolor" drop down
Pick one of the suggested colors ("light variations" work best), or hard-key a RGB color code from you color schema in the more variations/more colors box
This technique works particularly well with noisy images full of colors, or pages that contain a lot of logos with irregular colors. Not as elaborate as Adobe Photoshop, but sufficient for most situations.
Often, the colors of images do not fit the color scheme of a presentation. One solution to this is to "take out the colors" of the image and replace it with a monochrome overlay with the most important color of your color scheme. As an example I have added some nice blue to my title page picture. How to do it (PowerPoint 2007):