Many printers use this or similar schemes, printing faint yellow dots in a grid pattern on printed documents as a form of steganography, encoding metadata about the document into its hard-copy output. The watermarks, shown in the image above-an enhancement of the scanned document The Intercept published yesterday-were from a Xerox Docucolor printer. When they did so, the Intercept team inadvertently exposed its source because the copy showed fold marks that indicated it had been printed-and it included encoded watermarking that revealed exactly when it had been printed and on what printer.
When reporters at The Intercept approached the National Security Agency on June 1 to confirm a document that had been anonymously leaked to the publication in May, they handed over a copy of the document to the NSA to verify its authenticity.
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