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Basic Information

Microdots are printing so small that it appears as just a dot to naked eye, but actually conveys information if you know what you're looking for and/or have the right equipment. It's a form of steganography, the art of putting hidden messages in an object or other message. It is a common tool of espionage.

There are few different versions, and advances in technology keep opening up new capabilities.

A cluster of information, incredibly tiny and clumped together, could be placed on a page with other more obvious writing in a much larger font. You place such a cluster of data anywhere that a dot would not be out of place in that larger (in other words, normal-sized) font: at the end of a sentence; or atop a semi-colon or a lower case "i". To read such a hidden message, you'd need a good magnifying glass or microscope. If you're not looking at the document that closely, just reading the normal-sized text, you're unlikely to notice anything being out of place.

Such dots don't have to be put on a message. They're pretty small, so they could be hidden in an object. That object could then be left in a dead drop, or carried through a checkpoint with relatively little danger. (Relatively. Don't try this at home.) In theory, even if someone has you under surveillance or frisks you, they're probably checking for concealed weapons, flash drives or documents, etc. Some random innocuous item in your possession having a couple tiny dots on it is unlikely to catch anyone's attention unless they are not only very suspicious but also have a lot of time on their hands. You can even attach the microdots to objects carried by a third party - although retrieving them afterwards may be tricky.

Another version uses even smaller dots, which it gets away with by not packing data into each individual dot, but rather encoding the data by the location of the dots, likely by laying the dots out in some sort of (largely unnoticeable) grid. In this case, the dots can be so small that you probably won't notice they even exist. If you do spot them, you may think they're a random ink spatter or paper impurity. Even if you do find them, and suspect they are meaningful microdots, you still have to figure out how to decipher the coded placement of the dots.

And given how easy color-printing is these days, this sort of thing can be done with really pale dots. One version is currently implemented in many off-the-shelf desktop printers to secretly place an identifier that marks the serial number of the printer, alongside the date and time of printing, hidden on every printed page. This is used for security purposes, and can be used by police and government investigators to identify the people behind an internet leak, news leak, ransom letter, bomb threat, etc. The dots are essentially invisible to the naked eye, and to see them you need to shine a blue light on the document (and possibly also magnify) to make the dots stand out.

And in these days of laser-etchers and computer aided design, there are also microdots that aren't ink-based, but rather carved directly into objects. Some Automobile parts have such numbers to help identify stolen cars and chop shop operations.

Nazi spies in World War Two used microdots created by special camera kits called a Zapp outfit. J.Edgar Hoover publicly warned about them (and spread a fair amount of disinformation as well) as far back as 1946. After the war, they were also used for messages smuggled beyond the Berlin Wall. British authorities sometimes used the term "duff" to refer to microdots.


2. Pocket article on the secret dots your printers make on every page you print

Game and Story Use

  • Any espionage story is likely to see these used in one form or another. Any spy character will know a thing or two about them, even if they don't have the equipment to make them for themselves.
  • If you're players are just stuck on your mystery plot, and the whole story is grinding to a halt, you can use microdots as a way to craftily insert new clues into old evidence. Either ask the players for a new perception check, or prompt them to take a second look at some item they'd captured/recovered/found in a previous scene (or session), and when they do, tell them that they just now noticed a series of suspicious dots on the item. A few minutes with a microscope (and/or a blue light) and they can read or decode a secret message that reveals whatever part of the plot they'd been previously failing to understand. (Obviously, this only works in a game where this sort of thing is in-genre. Great for communist agents, but not particularly believable in the hands of goblins and orcs.)
  • Can also be a believable way to write a character out of a spy game. If the PCs are relying too heavily on a particular confidential informant, mole or embedded source, have that source send them letters or smuggle documents out of their place of work. The FBI or other counterintelligence program gets their hands on one of these documents, examines the hidden microdot watermark, and can reverse-engineer exactly whose desk it came from. Even if the PCs help them make a jail break, the source is now on the run and no longer able to provide the intel or assistance that was short-circuiting your game.
  • Microdots on otherwise innocent documents can be a great intro into a story - a pile of papers inherited or acquired as a bundle with some other junk turn out to have secrets dot coded onto them, whether Nazi treasure from WW2 or other secrets from later eras.
  • Presumably there must be techniques for locating and purging at least the standard microdots - alternatives might be sanitising a printer so that it doesn't microdot, disrupting the printer's internal clock so that it adds nonsensical copy-dates or embedding a serial number that doesn't match the one on the printer. Presumably any of these invalidate your warranty and it may be tricky to prevent the printer whinging about them in one of these remote servicing agreements that are all too common these days, or having one of these inevitable and apparently spurious software patches "fix" your sanitising.
  • This may also inadvertently turn up a stolen printer (albiet probably one stolen from a fairly high end source) as its microdots turn up in an investigation.
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