1. A method for detecting a demountable accessory in an image-forming device, the image-forming device comprising a controller, a print platen suitable for receiving a substrate, and a handling mechanism, the print platen having an optical sensor associated therewith to capture an image of an item on the print platen, the method comprising: the optical sensor capturing a first image; the handling mechanism carrying out an adjustment action, which is suitable for adjusting the position of a substrate on the print platen; the optical sensor capturing a second image; analysing the first and second images to identify any changes therebetween; analysing at least one of the first image and the second image to detect an accessory identifier; from the results of the analysing, determining the presence of an item on the platen and classifying that item.