Accessing the images in Codeigniter but restricting URL to non users

I have images on my server that are uploaded by users within a group. I want to restrict the access to these images publicly by typing the absolute URL to the image. Access to these images should only be granted if the user is logged in to the system.

I am using CodeIgniter as a framework, and would like the restriction to be on the controller rather than the view. Right now I could not fetch these images on the view.

Here is my structure:

      application
                - <images_folder>
      system