Especially if it caused dirty lenses in front of the mirror or the lens may make those dirty block light into CCTV makes images from CCTV cameras so blurry.
Especially if it happens in front of a dirty lens or a glass lens may be dirty, obscured the light that goes into making CCTV images from cameras that are not clear.
Especially if the impurity is the front of the lens or mirror lens may be made to the dirty they hide the light entering the camera to make the images from cameras is not clear.