The misleadingly so-called "Mantegna Tarocchi" was a 15th-century model book, containing 50 subjects in a pleasing contemporary style. The subjects included an encyclopedic, cosmological hierarchy from the estates of man through muses, the Liberal Arts, and Virtues, to the celestial Spheres. They were not by Mantegna, they were not Tarot cards, and in fact they were not cards of any kind. They were a series of prints intended and used as a model book for artists. Three editions were created. The earliest is known as the E-Series, the second is called the S-Series, and the third the Ladenspelder series. Albrecht Dürer also copied some of the images.) They have long been discussed by writers on playing-card history, and will be addressed from time to time in pre-Gébelin. Arthur M. Hind, who explained their purpose as a "pattern book", also demonstrated their terminus ante quem, the latest possible date for their creation, based on two pieces of evidence:
There are two important pieces of evidence which fix the date of the E series as before 1468 :- (i) Five of the prints are pasted in a MS. (a German translation of Fior di Virtu), which was finished 28th Nov. 1468. The scribe has written round the prints, and has in some cases let his lines pass over their margins, proving that they were not inserted later. (ii) Miniature copies (of the Emperor and Pope, and the throne from the Mars) in a MS. Of 1467, Constituzioni dello Studio Bolognese, in the Archivio di Stato, Bologna
The second example mentioned provides a textbook illustration of how model books were used, our topic du jour re the E-Series. As an example, the images to the right show a detail from figure #6 of the E-Series model book, the S-Series copy, and the Ladenspelder copy. The images below show a figure from the 1467 MS. and from one of Durer's copies. We can seen the similarities of subject matter, pose, and style, along with differences in style and rendering. The 1467 MS. Emperor mentioned by Hind is a very close copy of the E-Series Emperor. 
The Pope, however, is an even better illustration of how model books were used; it is not an exact copy. Using a model book does not mean that an artist is unskilled, nor that they are uncreative, nor that they are even representing exactly the same subject matter in any particular sense. They may be using a generic figure to represent a specific person, or an allegorical personification. They may only be borrowing certain elements of the model. In identifying a model, the question is not whether all elements were copied, nor whether new elements were introduced, nor whether things were changed, including the ultimate subject matter of the depiction. The question is simply whether one image was used as a model for the other. And that judgment must take into account all relevant evidence.
A Matched Pair of Popes
In both images, the E-Series Pope and the 1467 figure, representing Pope Paul II, we have a seated, beardless pope, with papal tiara, the keys of Saint Peter, and a book. In both figures the pope wears a cloak which is secured below the neck, thrown back over the arms to expose the hands and a cinctured robe underneath, then drawn back together over the knees. The keys are displayed at shoulder height, held in the raised right hand. The book is displayed perched upon the left knee, held in place by the left hand, resting on top. The toe of one shoe is conspicuously exposed from beneath the hem of his robes.
The subject matter and composition, the position of the hands, keys, and text, along with a single toe peeking out from the robes, constitute a unique constellation of details. For comparison, Robert V. O'Neill collected a number of pope images, (15 are shown on the page linked below), mostly seated and some with keys, from both Tarot cards and other sources. If you look, you will see that some are vaguely similar to these two images. None of them, however, fit that description.
ICONOLOGY OF THE POPE CARDS
http://www.tarot.com/about-tarot/library/boneill/pope
In addition, there is a striking and unique signature, the drapery of the outer cloak. A distinctive line (highlighted in red, above) is traced by the right side of the Pope's cloak. It falls below his arm in front of his chest, rises up and over his arm, drops vertically to knee level, goes across his knee, drops toward the floor and folds back exposing the lining, then descends at about a 30-degree angle to the floor. The idea that such a pattern would be precisely duplicated in two pictures of a pope, two pictures with other such striking similarities of design, simply by coincidence is absurd. This is a clear demonstration that either one work was modeled -- in part -- from the other, or both works derived from a common source.
Despite such obvious and distinctive similarities, one prominent online Tarot writer, (one who dismisses many of Hind's conclusions, including both the obvious fact that the E-Series was a model book and the terminus ante quem dating), insisted on his website that the two figures were clearly unrelated, and that it was nonsense, even disingenuous, to argue otherwise. (The reader can judge whether the present argument is nonsense, but it is certainly not disingenuous.) But there is still more to the analysis of the E-Series' image use as a model in this instance. As noted above, all relevant evidence must be considered. The Papa Paolo II figure is sitting on a throne derived from the chariot of Mars (E-Series figure #45). Behind him is a curtain copied from the E-Series Emperor, and the Pope is depicted in the same scene as a very precise copy of the E-Series Emperor. Standing at the Emperor's right hand is a Chevalier, illustrated above, modeled after E-Series figure #6. All this shows that the E-Series was used as a model book by the artist who painted the miniature, redundantly confirming the obvious debt in the case of the Pope.
This constellation of facts, taken as a whole, is a perfect illustration of the manner in which model books were commonly used. Things were borrowed, but not slavishly copied. They were altered in various details, put in larger contexts and narrative scenes, and even given different meanings, perhaps as a specific person or an allegorical personification. As always, context counts.
In this case, the new composition calls for the pope to be turned toward the center of the image, and his specific identity calls for the figure to reflect, in some degree, that of pudgy Pope Paul II with his fat face and double chin. Moreover, his outer cloak appears to have been modeled after another image, or a description of Pope Paul II, or perhaps even an actual viewing of the Pope. The E-Series figure has a neck, whereas the miniature is wearing a mantle that rises to the back of his head, making it appear that his shoulders nearly reach his ears. The variation from the model is readily explained by looking at this painting of Pope Paul II. The artist made changes to the E-Series image, and some of the more striking ones are readily explained. A group of changes were made so that the composition of the 1467 miniature would be strikingly symmetrical. This called for changes to both figures, the Emperor and Pope, from their E-Series models. As mentioned, the Pope had his body turned slightly toward the center, thereby reflecting the figure of the emperor. The Pope's head was inclined to match the Emperor. A scepter was put in the Emperor's hand, to mirror the Pope's keys, and the Emperor's orb was changed to a scroll, thus adjusting both figures to create the symmetric composition and establish the proper subject matter for the new work.
