Well that is exactly my point. The images in the database are just fine as usual, nothing corrupted there at all, but yours are. So, that leads me to believe its a issue on your end. If it was us, we would have thousands of different users screaming at us right now cause there images are bad. Instead we have just you.
Pick a small platform, like 32X and delete the whole Launchbox/Images/Sega 32X folder. Then click one game in the UI and CTRL A to select them all, then Tools/Download Metadata and Media, and check the media items you want.
What do you get when you download them?