Watermark

Watermarks vary greatly in their visibility; while some are obvious on casual inspection, others require some study to pick out.

In another instance, identifying codes can be encoded as a digital watermark for a music, video, picture, or other file.

[2] At the time, watermarks were created by changing the thickness of paper during a stage in the manufacturing process when it was still wet.

Traditionally, a watermark was made by impressing a water-coated metal stamp onto the paper during manufacturing.

The dandy roll is a light roller covered by material similar to window screen that is embossed with a pattern.

Because the patterned portion of the page is thinner, it transmits more light through and therefore has a lighter appearance than the surrounding paper.

Watermarks were nearly universal on stamps in the 19th and early 20th centuries, but generally fell out of use, but some countries continue to use them.

Stamp paper watermarks also show various designs, letters, numbers and pictorial elements.