The CDOT website addresses the issue:
cityofchicago.org/city/en/depts/cdot/provdrs/red-light_cameraenforcement.html
Click on Misconceptions vs. Realities; it is the next-to-last item.
All motorists who receive red-light camera tickets can view a video of the violation:
photonotice.com/login.asp?Citycode=chi
However, videos are only archived for a certain amount of time. Therefore, if this is an older ticket the video may no longer be available.