An image forming apparatus having an image forming part that forms an image on a recording medium measures, downstream of the image forming part in a transport path of the recording medium, speckles on the recording medium, and generates measured speckle data that represents speckles measured; stores the generated measured speckle data in a memory part, further measures, upstream of the image forming part in a transport path of a recording medium, the speckles of the recording medium; determines whether speckle data representing speckles analogous to speckles measured upstream of the image forming part is stored in the memory part, and, in the case where the decision result is affirmative, recognizes that the recording medium for which the speckles have been measured is a recording medium on which an image has been formed on it previous to having speckles measured upstream of the image forming part.