How to implement access permissions per individual field and individual nodes? I know there is https://www.drupal.org/project/field_permissions module, which allows to set field permissions per role, however what I need is to provide each individual field access permissions. As put on https://www.drupal.org/node/1376182 


  It looks that there is no module allowing to restrict access to
  certain files / images per role. What I think about is having
  checkboxes beside each file/image where to select the roles to have
  view access to the according entry.


I can't believe this was not implemented before, so hopefully someone can point out a viable solution. 

Edit: I've got couple responses confused about what I wanted, so I believe I have to elaborate little more.

Field Permissions set role permissions for the field across all the nodes. What I am looking for is role permissions for individual field PER NODE. For example, an admin for Drupal 7 site could edit node 1 and make the file attached to it viewable to role "subscriber", but that wouldn't change any permission for another file attached to node 2. I hope it is now clear.
Not sure if it is going to be the best/most elegant solution, but here is "an" approach that might work:


Use the Entity reference module to replace your file field in your existing content type with a reference to some other content type (say Resource).
Attach your files to nodes of content type Resource (so not in your already existing content type nodes).
Use the Content Access module to implement the refined access that you are looking for, but applied to that Resource content type.
Create some testcase(s) to verify how that refenced Resource node is going to be shown in your original nodes.


Get the idea? Pretty basic Drupal techniques (to KeepItSuperSimple, aka KISS).

I haven't tested it (yet) while writing this answer, but I bet functionally it will behave exactly as what you'd want. And guess what: no need for the field permissions module to make this work.

FYI: the above is a D7-equivalent of how I used to create such kinds of related content in D6 already (also using the Content Access module, and I believe in D6 it was "node reference" or something like that).