In accordance with an embodiment, an image processing apparatus comprises a conveyance section, a first image reading section and a detection section. The conveyance section conveys a sheet in a first scanning direction. The first image reading section reads an image of the sheet conveyed by the conveyance section per line of a second scanning direction orthogonal to the first scanning direction. The detection section, based on an image signal read by the first image reading section, detects a front end portion and a rear end portion of the sheet in the first scanning direction.