Canon has issued a service advisory for owners of Canon EOS Rebel T6s (EOS 760D) and EOS Rebel T6i (EOS 750D) cameras. The problem has been described as “white spots” on the optical layer in front of the image sensor. This can cause “dark circular patterns” patterns on images.
The problem may be present on cameras that have the digits 01 or 02 at the first two digits of their serial numbers. If your camera is affected, the advice is to contact your local Canon Customer Support Center.