Simplified object and scene filenames
Added scene mask option
Simplified and corrected discovery of corners. Correction was kind of a bugfix. If the projection was rotated or flipped, then top and bottom in the extracted image would be reversed and cause an error when indexing the original image to extract the result.
Added warnings / error+exit for many places that caused me confusion when I was learning how to use everything.
removed unused function
clarified area calculation function
Added another sanity check for the extracted image and a condition to ignore it when the dimensions are invalid for opencv.
Moved source images to a folder to keep files more clean.