A banknote acceptor illuminates a banknote as it passes through an evaluation channel in a manner to locate the banknote in the width of the channel. A photo sensor array receives reflected light from the surface of the banknote and has a series of responsive divisions across an illuminated banknote. These divisions are sampled and analysed according to the banknote position to determine the authenticity of the banknote. Both apparatus and method steps are disclosed.
