The present application is based on, and claims priority from JP Application Serial Number 2020-139957, filed Aug. 21, 2020, the disclosure of which is hereby incorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to an image forming apparatus that forms an output image including an authentication image for authenticity determination on a medium, and an image forming method.

2. Related Art

To prevent a fake printed material from being distributed, an output image including an authentication image for authenticity determination is formed on a medium. JP-A-2017-65009 discloses a plurality of print media to be posted on a product, on which a print pattern for authenticity determination is printed together with a product logo. On a base sheet for forming the plurality of print media, the print pattern is formed by a pair of printing rollers, and the product logo is formed by another pair of printing rollers. The printed base sheet is cut on a print medium basis.

When the plurality of print media are formed by, for example, the same individual printing apparatus, the plurality of print media are formed with the same print pattern. When the same individual printing apparatus is used for creating a fake print of the print media, authenticity of the print media cannot be determined. In such a case, anti-counterfeit measures are also required.

SUMMARY

An image forming apparatus according to the present disclosure is an apparatus that forms an output image including an authentication image for authenticity determination on a medium. The image forming apparatus includes: a recording head configured to discharge a droplet onto the medium; a drive unit configured to perform main scanning in which the recording head moves in a main scanning direction and sub scanning in which the medium is fed in a feeding direction; and a control unit configured to control, based on image formation data representing the output image, the main scanning and the sub scanning performed by the drive unit, and the discharge of the droplet performed by the recording head. The control unit performs a control to form the authentication image by a plurality of times of the main scanning in which feeding positions of the medium in the feeding direction are different, and performs a control so that at least one feeding amount of the medium in one sub scanning is different between a feeding amount at time of forming the authentication image and a feeding amount at time of forming a portion of the output image that does not include the authentication image.

An image forming method according to the present disclosure is a method for forming an output image including an authentication image for authenticity determination on a medium by performing main scanning in which a recording head that discharges a droplet onto the medium moves in a main scanning direction and sub scanning in which the medium is fed in a feeding direction. The image forming method includes forming the authentication image by a plurality of times of the main scanning in which feeding positions of the medium in the feeding direction are different. At least one feeding amount of the medium in one sub scanning is different between a feeding amount at time of forming the authentication image and a feeding amount at time of forming a portion of the output image that does not include the authentication image.

