A watermark is a faint design or image embedded in paper that you can see when you hold it up to the light. If you've ever examined paper money closely, you might have noticed a subtle picture or pattern that becomes visible when light shines through it. These marks are created during the paper-making process and are nearly impossible to copy, which is why governments use them on currency to prevent counterfeiting.

Banks, governments, and artists have used watermarks for centuries to prove that documents are authentic. If you hold a bill up to a light, you may see a watermark showing a portrait that matches the one printed on the front.

In the digital world, a watermark means something slightly different: a visible mark placed on photos or videos to show who created them. Photographers often put their name or logo on images to prevent others from stealing their work. Unlike paper watermarks that hide in the background, digital watermarks are usually visible, like a signature across a photograph.