Access groups based picture sizes

At the moment the size settings for thumbnails and pictures are connected. While this is probably good to keep it simple it would be great if one could allow certain groups to look at pictures but only at a certain size.

Lets say I have (as I indeed do) three settings "original", thumbnails 262 & pictures 0, "middle" thumbnails 182 & pictures 968, "small" thumbnails 121 & pictures 605.

Then I would like to be able to assign the "guest" group to only beeing able to view the "small" picture size, and only the "superuser" group to view the "original" picture size.

I'm not interested in limiting the thumbnail size. I would like everyone to be able to view all thumbnail sizes. However lets say a guest is viewing "original" thumbnails and opens up a picture. I would then like the application to check if the guest is allowed to view that size and if not check the next smaller size etc.

Since the quility settings isn't connected in a larger to smaller settings way (even though the ones that are there by default behaves in that way), I suppose it's not just a matter of adding security settings to the size but also some kind of priority if many settings are allowed to be viewed (or none).