microdot

thumb|NSA photo of microdots taped inside the label of an envelope. The envelope was sent by Operation Bolívar|German spies in Mexico City to [[Lisbon during World War II, but was intercepted by Allied intelligence.]]

A microdot is text or an image substantially reduced in size to prevent detection by unintended recipients. Microdots are normally circular and around in diameter but can be made into different shapes and sizes and made from various materials such as polyester or metal. The name comes from microdots often having been about the size and shape of a typographical dot, such as a period or the tittle of a lowercase i or j. Microdots are, fundamentally, a steganographic approach to message protection.