1. An image processing apparatus, comprising: a document type automatic discrimination section that, based upon image data read from a document, automatically discriminates a document type of the document, wherein the document type automatic discrimination section comprises: a halftone pixel quantity counting section that counts a halftone pixel quantity which is a quantity of pixels in the image data that belong to a halftone reproduction region; a photographic-picture pixel quantity counting section that counts a photographic-picture pixel quantity which is a quantity of pixels in the image data that belong to a continuous tone region; and a high density pixel counting section that counts a high-density pixel quantity which is a quantity of pixels in the image data, such that in each of the pixels any one color component takes on a value smaller than a predetermined threshold, wherein with reference to a counting result yielded by the halftone pixel quantity counting section, a counting result yielded by the photographic-picture pixel quantity counting section, and a counting result yielded by the high density pixel counting section, the document is discriminated as a specific inkjet printed image when TH1<the halftone pixel quantity, TH3<the photographic-picture pixel quantity, and TH4<the high-density pixel quantity are satisfied, TH1 being a threshold for determining whether or not the document is a photographic-picture document and indicating a minimum quantity of counted halftone pixels at which the document is not determined as a photographic-picture document, TH3 being a threshold for determining whether or not the document is a printed-picture document and indicating a minimum quantity of counted photographic-picture pixels at which the document is not determined as a printed-picture document, and TH4 indicating a maximum quantity of high-density pixels at which no deterioration in image quality is observed when a toner distortion occurs.