1. An image input device comprising: an image capture unit which captures an image of a predetermined image capture range to produce image information; an image analysis unit which, when a range specifier for specifying a partial range within the image capture range enters the image capture range of the image capture unit, detects the range specifier based on the image information, and determines the range specified by the range specifier; an expansion processing unit which performs expansion process for expanding the determined range of the image information produced by the image capture unit when the range is determined by the image analysis unit; and an image information output unit which outputs the image information subjected to the expansion process to the outside.