Can you tell me what type of database that the application runs on and if this requires shutting down before any nightly backup takes place?

The program uses apache derby as its database. It doesn't necessarily require shutting down to back it up. Setting a backup task for off peak period eg. 3am is probably the best idea.

The size of a scanned image is around 300kb. The database usage is around 500kb per form. The only thing you may need to do every now and then is to properly shut down the server as this will run the vacuum task a compact the database to reclaim the space of deleted records.