Add a File, Close menu item to make it easier to move from one image to the next when there are multiple images to work with.

It is a bit unclear at first that saving is *.sca, that one needs to export the file, and then either select a new file where it will ask if you want to save (.sca)
Intuitively, Save suggests the image, and an Image Close menu item would clarify. Also, modifying the File menu to clarify Save Scanned File instead of Save or Save As would also help.