The TWAIN Working Group provide C source code for a utility to investigate any TWAIN data source (commonly referred to as a driver).
We've built this code and fixed a number of errors and omissions.
TWACKER enables you to select a data source and check what TWAIN capabilities are really available. Most importantly, you can turn off the data source User Interface (assuming this mode is supported), and acquire images directly.
You can download this utility here.