According to one embodiment, there is provided an image forming device, the image forming device applying information differently for each copy to a sheet on which an image is to be formed. The image forming device includes a controller, an image forming processor, and an authenticator. The controller is configured to acquire image information, the image information including an input image to be formed on a sheet and applying information associated with each copy, in response to the input image being formed. The controller is configured to generate a composite image obtained by applying an applying image based on the applying information for each copy to the input image. The image forming processor is configured to form the composite image generated for each copy on the sheet of each copy. The authenticator is configured to authenticate a user based on a user identity.