The technique that I employ to qualify anotados is to use Corel Draw and align the subject anotado into my form and check several points of interest at one time. The first thing that I do when examining an anotado is to scan the image. I personally scan everything at 600 dpi just for consistency.
Corel Draw Template
Once I have captured the image of the subject I will isolate only the anotado overprint by rotating the image to get the "Anotado" baseline such that the image will be flat and aligned at the baseline. Many overprints can be immediately disqualified due to their length. If they are considerably narrower or wider than they should be then I would just disqualify them and classify them as counterfeit.
Notice that in my template above, approximately in the center of the image is a rectangle formed with a dotted line. Using Corel Draw (other draw packages may be used, I simply selected Corel Draw) I will import the subject overprint and drag it into the dotted rectangle.
Subject overprint in place
Once the subject is dragged into place, I can test to make sure that the various points of interest all line up properly. Above I intersect the left side of the "A", the center of the "n", the point where the "t" is crossed and the right side of the final "o".
Close up comparison
In the above comparison, the reference points are close but slightly inconsistent. First the shape of the "A" is different, even considering Jim Beal's two overprints. The "n" appears taller and is also a different shape from the genuine (just above). But overall, this is a good forgery that could fool most people.
Test these points and pay particular attention to the letters to make sure that they have the proper openings at the proper places. But basically, it is just a matter of comparing the overprint with a genuine. If they are the same then there is a good chance that the overprint is OK.
If you would like to have a copy of the graphic images of the template I will provide them for downloading using the following links.