1. An image reading apparatus comprising: an image data obtaining unit that obtains, as image data, a read signal read from a document that passes over a read area; a foreign material position information obtaining unit that obtains, as foreign material position information, a read signal read from the read area in which the document is not present; and a separation processor that separates the image data into a plurality of objects including a background object corresponding to a background of the document, detects, by using the foreign material position information, a streak image portion that is caused by foreign material present in the read area and that is included in the image data, and performs a process for assuming a pixel of the streak image portion to belong to the background object if the pixel is present in the background object and has a pixel value equal to or smaller than a threshold determined in accordance with a representative value of the background.