If you are referring to not using ODC/ODDC kind of software which has drivers to connect to Webcenter Content then following is what I can think of:
1. Have your scanner drop the scanned images to a shared folder
2. Have a standalone Java program to checkin the scanned images to Webcenter Content using RIDC API calls
3. Access what set of metadata you want to set on the content, advice you set most of the general metadata on the folder so the content inherits them
4. If the metadata is available in a database then you could use the Java program to look up to this DB for metadata which performing the checkin
I think Webcenter Capture can fulfill the requirement.
Check the link for more information:
Documentation available here