[1] Martínez de Espinar appears in the original version of Prince Baltasar Carlos in the Riding School painted by Diego Velázquez at the Palacio del Buen Retiro in 1636.

[2]: 272  He is shown in the right middle ground of the picture, handing a lance to Gaspar de Guzmán, Count-Duke of Olivares, riding-master to Prince Baltasar Carlos, who will then hand it to his charge, who is on horseback in the foreground; behind Martínez de Espinar is Juan Mateos, while on a balcony of the palace stand King Philip IV and Queen Isabel.

[1][2]: 272 Three portraits are known or believed to be of Martínez de Espinar: the frontispiece of his book Arte de ballestería y montería, an engraving by Juan de Noort [es], also known as Johannes van Noordt III;[3] an anonymous painting of the school of Velázquez in the Museo del Prado in Madrid, thought to be of him;[1] and another anonymous portrait in the Museo del Greco in Toledo.

The Arte de ballestería y montería is one of the three principal works on venery of the Spanish Baroque period.

[1][5] It is dedicated to Balthasar Charles, Prince of Asturias, and contains portrait engravings of him and of Martínez de Espinar by Juan de Noort; the other engravings, of hunting scenes, are by an unknown hand.