The files likely have custom icons which were created by your scanning program.
Select one of them and open the Inspector (cmd-shift-i). Select the icon in the top, left and press delete. The icon on the Inspector should return to a generic file icon and the OS will render the icon based on the image in the file.
You can then select the next image and the Inspector window will update to reflect what you have selected.
If you have a lot of them, you might be able to remove all with an Applescript. There is a Mac OS X Technologies forum where the Applescripters hang out.
Unfortunately I have hundreds and posted in the Tech dept as you suggested.
However, I then had second thoughts and selected ALL the photos, clicking cmd opt i and believe it or not, just one Get Info window opened representing all of them!
One deletion and every thumbnail was renewed.
WARNING TO OTHERS! Do not control-click all the pictures and select Get Info otherwise your desktop will be inundated with hundreds of Get Info windows.
I didn't populate my desktop with a thousand windows and you didn't get the keys wrong.
Both combinations seem to have the same effect in that multiple selections produce just one window.
I'm just puzzled why control clicking multiple items and selecting "Get Info" from the contextual menu results in multiple windows as they seem like the same commands?
I don't get anything with shift, only option.
Get Info used to work that way until they created the Inspector. Now, if you want to Get Info on a group of items, you use the Inspector. Regular Get Info will open a single window for every item selected.
I'm not sure how the contextual menu is any different; I don't see any on mine. Just regular and with option.