Where is Selected Source saved?

[JustinB]

One of the programs my company uses does not always use the appropriate device when scanning documents. The vendor suggested using IrfanView to set the default TWAIN source, as this default will be respected by their application as an override. Can someone tell me what happens behind the scenes when a Source is selected? Is this written to a registry entry, flagged in a config file somewhere, etc? My hope is to find out what their program is looking for so I can make these modifications without needing to use IrfanView each time.

(Disclaimer: Outside of this scenario, I am a proponent of IrfanView and do use it all the time for TWAIN troubleshooting )