The study of the meaning of images, including their symbolic content.
In general terms, the subject of a picture is called its iconography. More specifically, iconography is the study of the meaning of images, including their symbolic content. The eagle, for example, may be interpreted as a symbol of Christ (from its interpretation in the bestiary and related texts) or of the evangelist Saint John (see Evangelist symbols) and is linked in exegesis with the Resurrection.
Michelle Brown, Understanding Illuminated Manuscripts (Malibu, CA: J. Paul Getty Museum in association with the British Library, c1994).