According to an embodiment, a detection apparatus for detecting a decoloration ink image includes an image reading unit, a decoloration unit, and a controller. The controller acquires image data using the image reading unit before decoloration that is the image data on the sheet before decoloration processing is executed by the decoloration unit. In addition, the controller determines whether or not there is a difference between the image data to be decolored and the decolored image data, thereby determining whether or not the decoloration ink is used in the sheet.