change user permissions or content owner dinamically

Hi everybody,

im new on the group, im searching for orientation on a problem.

Just lest imagine that we have a content type written by a user (user1, role1), for example describing a place. Then, a different user (user2,role2) can upload images related to this place, let´s say for example using cck and comments to relate both contents in an easy way (maybe it could be done better, im studing this).

Then, what i need is that the user1 can modify the upload images of user2, but no any content of user2, just the content added to the content created by himself (user1).

Simplificating, user1 create a content, user2 comment the content of user1. Then user1 should have the permissions to edit, delete, etc... the content or the comments added to the content created by himself.

The problem is that user1 cannot has access to other content created by other user (user3) with same role.

Is it possible to do something like that? How or what documentation / modules should i read?

Thanks a lot in advance.