A microdot is a chunk of text shrunk to an extremely small size, almost to a dot of diameter 1 millimeter or even lesser using a special microfilm. The dots are barely visible and can get past most eyes undetected. When these microdots are used in conjunction with steganography, (embedding information inside other objects like a picture), it becomes almost impossible to identify their presence, thus providing an innovative way to conceal information from prying eyes.
The microdot technique, however, was born out of a simple necessity to send a large volume of messages using a single pigeon during the Franco-Prussian war in 1870. Rene Dagron, a French photographer came up with the idea of the microdot. This technique was put to use by the Germans during the World Wars and later on other countries utilised it to send classified messages through the normal postal services. Today, car-manufacturers employ a technique called microdot identification, not to send secret messages around in their factories, but to identify the parts of each car.
Tiny discs etched with unique identification numbers using laser are coated with an adhesive that shines under ultra-violet light and are sprayed onto the car at certain places. This prevents car thefts since the car can now be easily identified and mapped to the owner using the microdot tags, which are invisible under normal light. Further, it also serves as a check on the use of old and used car accessories on new cars.
- Wikipedia - Microdot
- Hot to make Microdots