Three relevant sculptures by Antonio Canova, housed in the Hermitage Museum of Saint Petersburg, were studied during their temporary exhibition, in different years from 1991 to 2008, in three Italian cities: Rome, Venice and Forlì. The Canova art works taken into consideration were: “The Graces” (1813), “The Hebe” (1795), and “Love Awaking Psyche with a Kiss” (1787-1798). We performed systematic observations by individually interviewing “in the field” many visitors viewing the three aforesaid works, in order to highlight and measure some vivid visual illusions. These are: the consistency that is visually attributed to the marble, appearing influenced by the meaning of what was portrayed; typical visual shape sub-constancy and rigidity loss when “The Graces” are observed slantwise; visual position sub-constancy, and rigidity loss, when “The Hebe” is observed in different orientations with respect to the beholder position; and apparent movement, with rigidity loss, of the spread wings of “Love” during the rotation on its own axis of the “Love and Psyche” marble group. In this respect, we also have a video clearly illustrating the phenomenon. Specific psychological measures were proposed and performed for these illusions.