Opens the Twain Data Source that was picked out via TwainSelectSource (or the default data source if none was previously picked).
Synopsis
error = TwainOpenSource(NumOfImages)
Args
NumOfImages is a count of how many images you're willing to accept from the data source, for example, 1 for only one image. If omitted, then this indicates that you're willing to accept as many images as the data source contains.
Returns
An empty string if a data source is successfully opened, or an error code not.
Notes
If TwainOpenDSM has not been previously called to open the Data Source Manager, then an error occurs. TwainQuery can be called to check whether the data source manager is open.