Display thumbs instead of Icon for all images.

I know that there is the option for a custom icon, but if you have a lot of images it takes hours...
It would be nice if you can implement this option for a theme (Checkbox, Display image thumbs instead of icon).
Right now there is no other plugin who can do that... and i tested a lot...

And the function for thumbs are already in WP... so I should not be a big thing..!? Right?