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HankronA 75x power microscope is strong enough. Offhand, I would the dark rim would be distinct.
When the paper or cardstock is rough, this rim might be obscured. In these cases, there is a second method for identifying photoengraving (type of printing used on Fro Joys) versus lithography or coputer printing (type of printing used to make reprints). Specifically, the dots in the half-tone are/were made differently and the photoengraving dot pattern is distinct and identifiable. However, I have not ever sat down and written an article/guide on that subject. At some point in the future I likely will, but it's not something I will tackle in the nearest future.