The device includes an illumination; a camera configured to acquire at least one image of at least one portion of a symbol, the running substrate being illuminated by the illumination; and a processor connected to the camera and configured to be suitable for implementing an image-processing step in which the acquired image is processed by the processor and decoded. The camera used is linear and the illumination is a dark field illumination. Furthermore, the device is configured to carry out, prior to the processor processing step, a plurality of image acquisitions with the linear camera of various portions of the symbol.