veneration of images
Images may be used to adorn, to instruct, to excite to piety by recalling the persons represented.
As images of sacred persons, they are treated with becoming reverence, even as the picture of one's mother would be.
Their representative character, on account of which the thing is lost sight of in the recollection of the person represented, leads naturally to bestowing upon the image the marks of reverence and love we would bestow upon the person himself were he present.
These are the natural foundations of veneration of images.
This process can be followed in the practise of the Christian conscience from the earliest times.
Images were used from the beginning, in the catacombs, in places of worship, in private homes.
In the East, where homage paid to the statues of emperors, like our salute to the flag, was the order of the day, this veneration developed early and freely; in the West, more slowly.
Saint Basil (379) enunciated the principle:
We must distinguish between absolute and relative veneration; that paid to images is relative, i.e., it refers to the original.
When the Iconoclastic heresy forced the Church to declare upon the matter, the Seventh General Council, the second of Nice (787), defined the Catholic position, distinguishing between divine (latreutical) adoration and veneration of honor (Greek: time), between absolute and relative veneration, the latter due to images, because referred to the original.
It declared the practise of the faithful and of the Church legitimate.
In 1562, the Council of Trent (session XXV) restated the doctrine in still clearer terms.
New Catholic Dictionary