This is basically no problem. Open a DS with a known name via DG_CONTROL / DAT_IDENTITY / MSG_OPENDS. Make sure that you set in TW_USERINTERFACE ShowUI to FALSE. Than just negotiate the capabilities you like to set.
The easy way is of course to use a 3rd party tool as we or others from the vendor list offer and call just:
twaincom c:test.jpg -r 300 -monochrome -paperformatusletter -usedriver “HP ScanJet 5500 Series” -o -p
Depends how much time you are willing to spend on TWAIN insides.
Best regards,
Kaij