The project representative users are the "first-contact" users for this project.
Their names and e-mails are displayed on the project Dashboard and will be visible by all the contributors of this project.

The project managers are the privileged users who can modify this project by adding or removing images, contributors, etc.
A project manager will also be able to delete this project!
Then, it must be a trusty person.

The project contributor are the normal users. They can't modify configurations of the current project.
Their permissions on images, annotations etc. are defined with the project Editing mode.