Patent ID: 7715038

Claim:
An image forming apparatus connectable to a network, comprising: an identification unit adapted to identify whether a digital signature is added to image data; an authenticity inquiring unit adapted to inquire of a signature authentication server connected to said network about the authenticity of the image data, if said identification unit identifies that the digital signature is added to the image data; a determination unit adapted to determine whether the image data is valid, on the basis of information transmitted from said signature authentication server in response to the inquiry or the presence/absence of a response from said signature authentication server; and an image forming unit adapted to form synthetic image data by adding, to the image data, data corresponding to a determination result from said determination unit, and form a synthetic image from the synthetic image data, wherein if the determination result shows that the validity of the image data cannot be certified because no response is returned from said signature authentication server within a predetermined time, said image forming unit forms synthetic image data by adding data corresponding to the determination result to the image data, such that information indicating that the validity of the image cannot be certified is formed on the synthetic image.