Dave, I think the easiest thing for you to do (if you have a lot of images sort of spread out among many playlists, etc.) is to do one of the following two things:
1. Go to "File...", "Library...", "Clear Library". This WILL NOT delete any of your files from your hard drive. It will only remove them from Media Center (they no longer appear in it). Then, go to "Tools", "Import Media..." and click the "Advanced" button to expose the hidden part of the small form that pops up. In the newly exposed portion of the form, you will see 3 small buttons on the right in the middle of the form. The first button has a checkbox icon that's checked, the second button has a checkbox icon that is unchecked and the third button has a "DEF" icon. First, click the SECOND button (with the unchecked checkbox) to clear out all the media file types Media Center should search for once you click the "Start Search" button (but don't click the "Start Search" button just yet). Next, scroll down the list of media file type associations and check the box next to each file type you wish for Media Center to import (alternatively, you could clear all the checkboxes by clicking the empty checkbox button, then click the button with "DEF" on it, which selects the default file types that Media Center will search for, then uncheck the file types that are associated with image files, such as .bmp, .gif, and .jpeg). Once you've checked the boxes next to the file types for which you want Media Center to search, click the "Start Search" button and Media Center will only search for files in the specified directory that have the file extensions that you selected. That's it. You're done.
2. Or, instead of clearing your existing Media Center library, you could expand the main "Media Library" node, then select the "Images" node (click on the word "Images" itself; don't expand the "images" node). This will list all of the image (.bmp, .gif, .jpeg, etc.) files that were imported by Media Center when you conducted your initial search. Press the "Ctrl" and "A" keys and this will highlight (select) all the image files shown on the right side of the screen. Press the "Delete" key and a dialog box will pop-up asking if you want to (1) Remove the files from Media Center, or (2) Remove the files from Media Center AND delete the files from your disk by placing them in the "Recycle Bin", or (3) Remove the files from Media Center and PERMANENTLY delete the files from your hard disk, which bypasses the Recycle Bin and deletes the files beyond recovery (well, sort of). It sounds as though you would want to choose the first option, "Remove from Media Library".
I hope this helps. If not, post again and I'll (or someone else) will try to help.
Wobbley