Long considered a copy of a Rembrandt, this red ink portrait from the National Gallery of Scotland has been verified as a Rembrandt. Depicting Jan Cornelis Sylvius, a preacher from the artist's town of Amsterdam, the work is considered by the hand of Rembrandt because it was pulled from an etching plate that was created by the Old Master himself. Even though it was printed posthumously, the print is still considered a Rembrandt and, thus, holds particular merit in the printmaking world and in art history. It was likely inked in the 18th century, when red prints were all the rage.
The following print, from the Art Institute of Chicago, is similar in character to the red one above. But, its granular differences, tonal distinction, and overall grainy appearance detract from the clarity and quality of the work. Thus, this apparent copy of the original 1633 plate, too, is classified as "a Rembrandt" even though it is derivative and, presumably, made after the original plate had been created.
Finally, consider the print below, from the collection of the Cleveland Museum of Art. Made in 1646, it borrows in subject and composition from the earlier two works above. The Cleveland piece is considered reproductive and illustrative, and yet, it, too, is a Rembrandt.
Seeing is believing: it's a wonder that it took the National Gallery in Scotland so long to realize that their print was pulled from the very plate that Rembrandt had etched. We tend to think that works created by Old Masters have an aura. And, yet, clearly, we can't always see what we should really believe.