An image forming apparatus comprising: an image forming device configured to form an image on a recording medium; and an image scanning device configured to generate scanned image data by optically scanning an image and transmit the scanned image data to the image forming device; wherein: the image forming device includes: a receiver configured to receive at least one of external image data transmitted from an external device and the scanned image data transmitted from the image scanning device as input image data; a first image forming unit (2Y, 2M, 2C, 2K) configured to form a developer image based on the input image data on the recording medium; a second image forming unit configured to form a mark image on the recording medium with luminescent developer containing a luminescent material so that the developer image and the mark image are formed on the same recording material, the luminescent material emitting visible light; and a controller configured to determine whether to make the second image forming unit form the mark image or not depending on a type of a transmission source of the input image data, the type of the transmission source being the external device or the image scanning device. an image forming device configured to form an image on a recording medium; and an image scanning device configured to generate scanned image data by optically scanning an image and transmit the scanned image data to the image forming device; wherein: the image forming device includes: a receiver configured to receive at least one of external image data transmitted from an external device and the scanned image data transmitted from the image scanning device as input image data; a first image forming unit (2Y, 2M, 2C, 2K) configured to form a developer image based on the input image data on the recording medium; a second image forming unit configured to form a mark image on the recording medium with luminescent developer containing a luminescent material so that the developer image and the mark image are formed on the same recording material, the luminescent material emitting visible light; and a controller configured to determine whether to make the second image forming unit form the mark image or not depending on a type of a transmission source of the input image data, the type of the transmission source being the external device or the image scanning device. a receiver configured to receive at least one of external image data transmitted from an external device and the scanned image data transmitted from the image scanning device as input image data; a first image forming unit (2Y, 2M, 2C, 2K) configured to form a developer image based on the input image data on the recording medium; a second image forming unit configured to form a mark image on the recording medium with luminescent developer containing a luminescent material so that the developer image and the mark image are formed on the same recording material, the luminescent material emitting visible light; and a controller configured to determine whether to make the second image forming unit form the mark image or not depending on a type of a transmission source of the input image data, the type of the transmission source being the external device or the image scanning device.