I created a new project for external testers to use which is a copy of a project we use internally. I restricted access to the external testers could not see the other projects. When they log in and view the test cases in the project they have access to they can’t see the images. The only way for them to see them was for me to give them at least read-only access.
I would think when you copy the test cases that the images should be available to that new project