Hey guys, I was having the exact same problem... I effed around for a bit and found a solution that fixed it for my external HD, not sure if it will be the same for yours, but give it a shot:
1. Go into the folder that won't display the image
2. Right click in the white/empty space and click "Properties"
3. Click the "Customize" tab
4. At the bottom under "Folder Icons" click the button "Change Icon"
5. Click "Restore Defaults", "Apply", "Ok"
It should now show a picture of all the files within the folder.
To select a specific image:
1. Go back into the folder
2. Right click in the white/empty space and click "Properties"
3. Click the "Customize" tab
4. Under "Folder Pictures" click "Choose File"
5. Find the picture you want then "Open", "Apply", "Ok"
This is what worked for me, hopefully it does the same for you, good luck.