The subject of Icons is always discussed in any good catechism.
Basically Christ gave us the first icon, The Icon Not Made By Human Hands.
The Armenian King had leprosy and he sent one of his servants, an artist, to capture Christ's face on canvas, but the artist could not. This happened before Christ was crucified. Christ had mercy on the artist and touched the canvas to His Divine Face and the image was transferred. This first Icon of Christ was then taken to the King of Edessa who was instanteously healed of his leprosy. The King then offered Christ asylum in his country, but Christ refused knowing that He must suffer and die for us.
This Icon was apparently lost when the muslims took over Constantinople where it was stored (unless the Vatican has it stored away in its archives).