Protecting Uploaded Media within networks

So, I understand that I can place noimageindex in my header to prevent search engine from indexing my images However, I would like the images that are published on individual blogs on my network to be indexed.

I just don't want upload images in the upload media directory to be indexed. I hope that makes sense. I guess to be technical I want all "unattached" images in Upload directory to be NON-indexed by search engines but all images that are uploaded AND "attached" to a blog post or page to be indexed.

Is this at all possible? I just want my users to be able to upload private images simply for storage and not for the general public to see UNLESS they specifically give a friend their link directly.

Thanks for your help everyone!

Mike