1. A security element ( 1 ) comprising a reflecting, optically variable surface pattern ( 11 ) which is embedded in a layer composite ( 3 ) of plastic material and which can be visually recognised from predetermined observation directions, formed from a mosaic of surface elements ( 12 ; 13 ; 14 ) with optically active structures ( 4 ), characterised in that a part of the surface pattern ( 11 ) is divided in accordance with a regular matrix ( 18 ) into cells ( 15 ) of equal size, that each cell ( 15 ) is occupied by a single elementary surface ( 18 ) or a group of identical surface portions ( 17 ), the elementary surfaces ( 16 ) and the surface portions ( 17 ) contain an optically active structure ( 4 ) which is independent of the mosaic of the surface pattern ( 11 ), provided in the matrix ( 18 ) are at least five cells ( 15 ) per mm, the diameter of the elementary surfaces ( 16 ) is less than 0.2 mm and a largest dimension of the surface portions ( 17 ) is less than 0.04 mm, wherein the elementary surface ( 16 ) or the group of the surface portions ( 17 ) occupies an equal surface area proportion in the range of between 40% and 70% of the cell ( 15 ), and the arrangement of the elementary surfaces ( 16 ) and the surface portions ( 17 ) in the matrix ( 18 ) forms an item of concealed information which is not perceptible to the naked eye, being in the form of graphic or alphanumeric characters which however are reproduced in a color photocopy with a color or gray value contrast which can be recognised with the naked eye and which is produced upon copying as an artefact.