TWAIN Functionality:  Callbacks

LTWAINBITMAPCALLBACK

LTWAINCAPABILITYCALLBACK

LTWAINSAVECAPCALLBACK

LTWAINSAVEERRORCALLBACK

LTWAINSETPROPERTYCALLBACK

LTWAINSOURCEINFOCALLBACK

LTWAINACQUIRECALLBACK

LTWAINDEVICEEVENTCALLBACK

LTWAINTEMPLATECALLBACK