Canon 9900f scanner glass removal

I would not worry about the underside of the glass unless you are having problems. The focal length of the ccd that captures the image is very specific and probably will not pick up anything under the glass. It is normal for the underside to look foggy but it will not hurt anything.

To be clear, it is quite easy to remove the glass, but you shouldn't need to even if you can see the odd bit of dust. However, if you do want to (voiding warranty etc.) here's how:

1. unplug and remove lid
2. use philips screwdriver, remove screws in the two recesses of the main scanner body that the lid hinges slot into
3. gently pry the black plastic part away from the grey plastic body, starting near the glass until it tilts up and away. be careful of the clips at the back end of the scanner
4. the glass panel and grey surround can then be lifted and slid towards the back of the scanner and pulled free.