Techniques for dynamically distributing short messages include storing action data and parameter data. A switching circuit switches the input of an evoked response sensing channel to an unselected electrode. Each record includes an image file section reserved for storing the image, an image metadata section reserved for storing data about the image, and a record metadata section having a status flag or status mark indicating whether the image file section is empty. A start point determination unit classifies the projection area based on a combination of the edge coefficient, and determines scan start point and scan performing direction of the bounding box in accordance with the classification.