Abstract: The apparatus is particularly suited for identifying mould cavity numbers formed in binary code in the stippling on the base of glass containers. It comprises light beam detection means (2), such as a photodiode array, which scans an area of the article to provide an output characteristic of the code; means (12) are provided for creating at least one window in time within each scan period by selecting which diodes in the array commence and terminate the window. Only output signals from the light beam detection means within the window in time are decoded to provide the code on the article. Preferably, the window is selected manually, e.g. by thumbwheel stores (14), and, further, a true decoding is arranged to arise for "1" in the binary code (presence of a stippling mark) only if a predetermined number of photodiodes within the window are activated at any one time. This true decoding reduces errors due to refraction of light from defects in the glass.