Solution
If certain kinds of black stains, dots, or dust are always visible in the same areas on images captured with the camera, dirt or dust may have adhered to the image sensor (CMOS).
Clean the image sensor to prevent dust from appearing in images
When changing the lens on the camera it is possible for particles and dust in the air to become attached to the image sensor depending on the environment and situation.
Although it is not possible to completely prevent this phenomenon due to structural reasons, the image sensor can be cleaned when you think there might be dust on it.
IMPORTANT
If the dirt or dust cannot be removed using the above methods, please consult a Canon repair center.
Removing dust from images using the Digital Photo Professional software
The Digital Photo Professional software that came with your camera* has a function that you can use to remove unnecessary spots (dust and dirt) in images and blend those areas in with their surroundings. For details, please see the Digital Photo Professional instruction manual.*
*If the abovementioned items (Digital Photo Professional software/Instruction Manual) were not included with you camera, please download them from the Canon homepage.