Client forensic watermarking device, system, and method

A forensic watermarking method performed by a forensic watermarking device capable of communicating with a content server comprising a second processor configured to select a watermark mask area in which a watermark mask is displayed from video content and store watermark area information about the watermark mask area in a memory, the forensic watermarking method comprising:

• a step of requesting the video content to be played from the content server and receiving the video content and the watermark area information from the content server;
• a step of outputting the watermark mask using the watermark area information received in the receiving step;
• and
• a step of superimposing the watermark mask outputted in the outputting step on the watermark mask area of the video content received in the receiving step,
• wherein the receiving step comprises further receiving a client session ID from the content server,
• the outputting step further comprises generating and outputting the watermark mask using the client session ID received in the receiving step,
• the generating step further comprises generating a mask frame comprising the watermark mask,
• by synchronizing the mask frame with an image frame comprising the watermark mask area, of the video content, the superimposing step further comprises superimposing the mask frame generated in the generating step on the image frame, and
• the mask frame is divided into a background and a foreground, and different alpha values representing a transparency level are imparted to the background and the foreground for invisibility.