Here is a straight-forward question of gross anatomy. The heart has 4 valves.
The heart has two main types of valves: semilunar and atrioventricular. Semilunar valves include the aortic and pulmonary valves. These separate the ventricles from the great arteries, and open/close passively to preserve unidirectional blood flow. The cusps distend with backflow from the aorta and pulmonary artery, much like wind catches in a sail, resulting in valve closure. The photo in our question is an example of a semilunar valve. This is in contrast to atrioventricular valves, which include the mitral and tricuspid valves. They separate the atria from the ventricles and are composed of leaflets and a tensor apparatus (the tendinous cords and the papillary muscles).
To distinguish between the pulmonary and aortic valve with just the image in the question, the anatomy of the outflow tract becomes important. While the valves themselves are similar, the pulmonary valve has an entirely muscular outflow tract (see arrows in this image). In contrast, the left ventricular outflow tract has a musculo (arrows)-membranous (asterisks) architecture just below the aortic valve, providing the important clue to this question’s answer.