Scratch

Hi all. I'm working on a very large game at the moment and as a result, I'm storing a lot of the images in folders that go with the game. However, as they are images of the game layout, someone need only open the folder to view all the levels. Is there some way of storing images in a format that won't come up as an image but can still be imported into Scratch (Panther) as an image?

The obvious option would be to store the image in a sprite and store the sprite in a file, importing it when needed but due to the Custom block warning popping up every time i import an image, it's not a neat solution at the moment.

Thanks!