Image forming apparatus

1. An image forming apparatus comprising:

an image forming device which forms an image on a recording medium; and

an image scanning device which transmits scanned image data generated by optically scanning an image to the image forming device; wherein:

the image forming device includes:

a receiver which receives 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 which forms a developer image based on the input image data on the recording medium;

a second image forming unit which forms a mark image on the recording medium with luminescent developer containing a luminescent material, the luminescent material emitting visible light; and

a controller which determines 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.

2. The image forming apparatus according to claim 1 , wherein the luminescent material transits from ground state to an excited state by receiving energy.

3. The image forming apparatus according to claim 1 , wherein the luminescent material transits from ground state to an excited state by receiving ultraviolet rays.

4. The image forming apparatus according to claim 1 , wherein the controller makes the second image forming unit form the mark image when the type of the transmission source is the image scanning device.

5. The image forming apparatus according to claim 4 , wherein the mark image formed by the second image forming unit when the type of the transmission source is the image scanning device includes at least one of a letter, a figure, and a symbol indicating that the transmission source is the image scanning device.

6. The image forming apparatus according to claim 1 , wherein the controller does not make the second image forming unit form the mark image when the type of the transmission source is the external device.

7. The image forming apparatus according to claim 1 , wherein when the type of the transmission source is the external device, the controller makes the second image forming unit form the mark image indicating the type of the external device as the transmission source.

8. The image forming apparatus according to claim 7 , wherein:

the external device is one of a facsimile machine, a personal computer, and an information storage device, and

the mark image formed by the second image forming unit when the type of the transmission source is the external device includes at least one of a letter, a figure, and a symbol indicating one of the facsimile machine, the personal computer, and the information storage device as the type of the transmission source.

9. The image forming apparatus according to claim 1 , wherein the second image forming unit forms the mark image in a printable region on the recording medium in which the first image forming unit forms the developer image.

10. The image forming apparatus according to claim 1 , wherein the second image forming unit forms the mark image in a marginal region on the recording medium other than a printable region in which the first image forming unit forms the developer image.

11. The image forming apparatus according to claim 1 , wherein on the recording medium, the mark image formed by the second image forming unit is formed as an upper layer on the developer image formed by the first image forming unit.

12. The image forming apparatus according to claim 1 , wherein the mark image is transparent under visible light and is visually recognizable when irradiated with ultraviolet rays.

13. The image forming apparatus according to claim 1 , wherein the luminescent developer is fluorescent toner which emits light by being irradiated with ultraviolet rays.

14. The image forming apparatus according to claim 1 , wherein the developer image based on the input image data is formed with toner.