I cannot access the image with my test report (the link goes to a 404 error page)

This is due to a privacy setting on the form owner's account requiring logging in to access uploaded files.

That needs to be unchecked as explained here: https://www.jotform.com/help/673-how-to-unrequire-log-in-to-view-uploaded-files/

Once that is done, you will not get the 404 error.

Please try and let us know.