Try both steps below to remove the image.
1st, select an image that you want as your desktop background. You will use it for both steps below
2nd, set the image you selected as the desktop background image using the method in the video tutorial below
http://www.cleartechinfo.com/Learn-How-To-Add-Change-Windows-Vista-Desktop-Background-Image3rd, set the image you selected as the desktop background image using the free software FastStone Image Viewer. The video tutorial will show you how to perform this step using FastStone
http://www.cleartechinfo.com/Learn-FastStone-Image-Viewer-Beginner-Basics-How-To-Guide