for your #2 problem, it seems to me that you need to verify that an image exists before enabling the device. for a twain solution take a look at the file related triplets. in appendix A there is an section “File System”, it’ll show you how to check if files exist using MSG_GETFIRSTFILE MSG_GETNEXTFILE. if your device doesn’t suuport those caps, then you might be able to verify this with stand io calls. .. or I’ve misunderstood the problem.
for #1, walk me thru the rough logic opening enabling disabling and closing the device with how that relates to the user taking shots.
and I wonder, why use twain here? I’m assuming you have the device connected and most devices that I have are mounted as a drive when connected. Couldn’t you use standard io calls to pull images off of the device as soon as they become available? Are you using twain calls to take the shots or just pull them once they’ve been taken? Do you use any twain calls to configure the device (set brightness etc,)? or are you trying to setup some automation?