This tempera on wood, created by Duccio between 1308-11, shows Judas as he identifies Jesus (by kissing him on the cheek). Peter (on the left side of the painting) reacts by cutting off the ear of one of the men.
The original work - entitled Christ Taken Prisoner - is located at the Museo dell'Opera del Duomo, in Siena, Italy.
Click on the image for a better view.
Image online, courtesy Web Gallery of Art.