Correct - this wouldn't be that hard, I thought so. Except we were running on embedded system, and taking photos will compete printing process for some system resource, causing some printing defects.
However, that was the time we were using OpenCV to take photos, on the maximum it can achieve poor 3fps - now we are using v4l2 and can achieve 3x speed in taking photos, as well in scanning.
So if anyone were developing embedded system and using camera, don't use opencv for product. It has terrible performance, unless you're doing prototype.
Since this big refactor may affect scanning reliability and the stability of whole system, we're still testing it to see if it works in most scenario. This feature will be merged into a new firmware update in 2 weeks hopefully.