This seems like a major project in and of itself but some initial thoughts..
Theoretically a scanner driver could have an API that would allow you to control the scanner. You could then scan to a file via the API and load either store a link to the file or the file itself in the database. Come to think of it I think there is a common API for scanners... TWAIN. You can research that.
A lot less work is probably to have the user scan to a file and then use a Windows API call to the open file dialog to select the file but more work on the user.
Another solution might have the database write the customer details somewhere where a .Net written service that monitors the scanned document folder, picks up the customer details, and writes the file to the database with customer details.