Watermark

A watermark embeds information imperceptible to human senses into content - images, video, audio, or documents. Like banknote watermarks that prevent counterfeiting, digital watermarks protect copyright, detect tampering, and trace origins.

QR codes and watermarks interact in two ways. First, embedding watermarks within QR codes themselves. Subtle modulations in module placement create visually identical codes carrying hidden verification data, enabling counterfeit QR code detection by authorized parties.

Second, QR codes as watermark alternatives. Traditional product authentication relied on physical watermarks requiring expert inspection. QR codes with serial numbers let consumers verify authenticity instantly by scanning and checking against a server database.

Advanced research explores steganography - invisibly embedding QR codes within ordinary images. A photo appears normal to the naked eye but reveals a QR code when captured with a specialized app, preserving advertising aesthetics while embedding information.