问题
I have a paper document that will be scanned, and then I'll want to perform image registration (image alignment) on different scans of different copies of the document.
I've noticed that paper forms often have a "registration mark" printed in the four corners of the piece of the paper (a cross-hairs: a circle with a plus intersecting in it). It looks something like this:
In my case, I have the freedom to choose the exact shape of the registration mark, to make it as easy as possible for the image processing code to detect the location of the four registration marks. My goal is for the code to detect registration marks as efficiently and robustly as possible, given that the image might be slightly rotated/skewed/translated. Is the "cross-hairs" shape shown above optimal? Are there better marks that are easier to algorithmically locate?
Black-and-white only; I can't print or scan in color, unfortunately.
来源：https://stackoverflow.com/questions/43404255/registration-mark-to-support-image-registration