This is a detail from Hieronymus Bosch's painting Triptych of the Temptation of St. Anthony (c1501).  On the left panel portrays the legendary flight and the fall of St. Anthony. The centre panel exemplifies St. the temptation of St. Anthony. On the right panel it depicts the Contemplation of St. Anthony. The two figures portrayed on the postcard obtained the ability to fly by the Devil in order to partake in  Witches' Sabbaths.