1. A processor-implemented method for processing image data using an image processing apparatus, the image processing apparatus comprising at least one processor for processing documents containing image data comprising a plurality of pixels, the method comprising the following acts implemented by the at least one processor: providing a billing structure comprising a plurality of original billing tiers defined by predetermined thresholds at which to bill image data; receiving image data of a document comprising a plurality of pixels; determining pixel classifications and counts of the pixels for each pixel classification in the image data; classifying the image data into a category or class based on the determination of the pixel classifications and the counts; determining counts of pixels for marking to output the image data; selecting one billing tier from the plurality of original billing tiers for which to bill the image data, and adjusting from the selected billing tier to a different billing tier for which to bill the image data using at least the category or class of the image data.