Student submissions with comments; multi-thread?

Here's the scenario we're looking for:
*Student submits a node
*This node has an image field and a text field
*They can upload as many images as they want (usually like 3-5) and they submit some text about the group of images
*Other students come in and give comments specifically about images that they submitted OR about their textual description of their artworks
*Teachers can read and respond to all comments / approve / disapprove of them for all to see

Now, i've got the student assignment node done with a simple title, body, and imagefield done. I've also got node-comments on so that I can add an approve / disapprove field and then use CCK permissions to only allow instructors to be able to set the approve/disapprove status (this is different from publish / unpublish comments because students need to be able to see what was / wasn't accepted).

What i'm having trouble figuring out is a way to allow for commenting per field (essentially). Students need to be able to have discussions about each piece of artwork individually and have them grouped together. I'd use gallery but I don't like the whole gallery thing and it also isn't nearly as userfriendly as "submit assignment 1" and then they just do it all in one space. It also centralizes things for review by the instructor. Any ideas? Is there anything out there that allows for multiple threads of discussion on the same page / node? Or has anyone else put together anything similar in which they did it another way with the same general affect?

I'm kinda at a dead-end with it and don't want to write anything custom if something exists that could help.