1. An acquisition system for acquiring an image of veins of a finger, comprising a camera designed to acquire an image of said finger when it is passed in front of it, a lighting device designed to illuminate said finger; a control unit for controlling the intensity of illumination of said lighting device; and at least one system for measuring the transmission power of said finger; upstream of the camera with respect to the passage of said finger towards said camera, wherein said control unit is designed to control the illumination intensity of said lighting device according to the transmission power measured by said measuring system.