On the left, a reproduction of the Mona Lisa with a representation of two vectors superimposed on top of it. The red arrow represents a vector in three dimensions pointing directly up on the plane of the painting and the blue arrow represents a unique arbitrary vector on the painting. On the right is the result of a shear transformation on the image on the left. The blue arrow now represents a different vector, while the red one still represents the same vector. For this reason, the red vector is an eigenvector of the transformation, and the blue vector is not.