How do I maximize scanning area in TWAIN?

My users tend to insert their paper in the scanner feeder somewhat randomly, and the开发者_开发知识库 default setting of A4 sometimes doesn't cut it - part of the image is cut away. How can I tell TWAIN to scan as big an image as possible?

I'm using EZTWAIN classic. I cannot find there appropriate function for that, and buying EZTWAIN Pro is out of question, so probably the only way is to talk directly with TWAIN.

Please help.

call TWAIN_SetPaperSize before calling TWAIN_SetRegion
Refer to Page 133 and 136 in www.dosadi.com/pub/eztp/EZTwain_User_Guide.pdf