1. A method for detecting an image corresponding to at least a monetary banknote, comprising: selecting a detection procedure from a plurality of different detection procedures, wherein the plurality of different detection procedures comprises a low-level detection procedure for determining whether the monetary banknote is a currency or not, a middle-level detection procedure for determining a currency type of the monetary banknote, and a high-level detection procedure for determining a currency type and a currency value of the monetary banknote; and verifying the image according to the selected detection procedure.