A visual tag having an imprinted image, a processor for calculating a response string corresponding to the content of the imprinted image and a challenge string, and a changeable screen to display the response string in machine-readable symbols. A global conversion rate is defined that represents activity related to a purchase made or proxy activity executed during electronic commerce traffic to a commercial website that is indicative of non-fraud activity. In this embodiment, the signature corresponds to the circuit’s response to no more than one test pattern. The DMA controller is equipped with a format converter converting the fixed-point type of digital data to a floating-point type of digital data. In an abnormally pressurized state, the power supply to the electromagnetic solenoid is shut off, to forcibly close the check valve.