How to scan with Canon D646U :

1. Open Photoshop
2. Click on File -> Import -> Canon D646U
3. Click preview. Preview will shown. After that click Scan.
4. Close the dialog box.
5. Picture is ready in the canvas.

Before doing that steps, don't forget to turn the scanner on, and then
connect it to the computer. If you don't have driver, you can download
it on http://support-sg.canon-asia.com/. Don't worry, it's free.

Just choose 'Scanners -> Others -> D646U -> Drivers and Softwares'.