1. An image determination apparatus which determines whether inputted image data is document image data or non-document data, comprising: a binarization process section which converts the inputted image data to binary image data by binarizing the inputted image data, and calculates a total black pixel ratio that is a ratio of a number of black pixels to a number of all pixels in the image data; a feature extracting section which detects connected components that are groups of pixels having a same color in the binary image data and circumscribing bounding boxes of the connected components, and generates a histogram by specifying the sizes of the circumscribing bounding boxes as classes and numbers of the connected components as frequencies of occurrence; and an image determination section which determines whether the inputted image data is document image data or non-document image data based on information related to the generated histogram and the total black pixel ratio.