Hiding messages in plain sight is not a new idea. Long before digital images and pixel manipulation, people were finding ingenious ways to conceal information where no one would think to look. The methods changed with the technology available, but the core challenge was always the same: make the secret invisible without making the carrier look suspicious.
Here are some of the most remarkable examples throughout history.
The historian Herodotus describes a method used by the Greek ruler Histiaeus: he shaved the head of a trusted slave, tattooed a message on the scalp, waited for the hair to grow back, and then sent the slave to his intended recipient. When the slave arrived, his head was shaved again to reveal the message. The method is slow by modern standards, but it worked — no one inspects a slave's scalp for secret correspondence. Herodotus also describes messages hidden in the wax of writing tablets, with the actual message inscribed in the wood underneath.
Chinese spies and diplomats reportedly used silk — writing messages on thin pieces of silk, rolling them into balls, and coating them in wax. The wax ball could be carried internally by a courier or hidden in food. Messages were also reportedly written in rice, where the arrangement of grains in a bowl conveyed meaning to those who knew the code. These methods blurred the line between steganography and cryptography, since knowing what to look for was itself the key.
Invisible ink became a staple of espionage and secret correspondence during the Renaissance, with methods ranging from the practical to the elaborate. Lemon juice, onion juice, and milk were commonly used organic inks that become visible when heated — the sugars in the liquid caramelize and turn brown. More sophisticated methods used chemical reactions: a message written with one chemical would only appear when the paper was treated with a second chemical. Invisible ink remained in active use through World War II and beyond.
Johannes Trithemius, a German abbot and polymath, wrote a book called Steganographia — the work that coined the word. On the surface it appeared to be a guide to summoning spirits through mystical rituals; scholars later discovered it was actually a codebook for concealing messages, with the magical incantations serving as carriers for hidden text. Trithemius also developed an early steganographic cipher called the Ave Maria cipher, where messages were concealed within innocuous-looking Latin prayers.
During World War I, Belgian resistance members reportedly passed military intelligence to the Allies through women knitting near railroad lines. Specific knitting patterns encoded information about troop movements and train schedules. Acrostic messages — where the first letter of each word or sentence spelled out a hidden message — were also used in letters that passed through censorship, since censors reading for obvious content often missed the hidden structure. British intelligence eventually trained censors to check specifically for acrostic patterns.
The microdot was one of the most technically impressive steganographic achievements of the 20th century. German intelligence developed a method of photographically reducing a full page of text down to the size of a printed period — a dot so small it was indistinguishable from ordinary punctuation. The microdot would then be pasted over a period in a letter or document and mailed to its destination. FBI Director J. Edgar Hoover called it "the enemy's masterpiece of espionage." When the FBI finally identified the technique in 1941, finding microdots in intercepted correspondence became a major intelligence priority.
A null cipher hides a message within an innocent-looking piece of text, with the real message encoded in a specific pattern — every fifth word, every third letter, or only the letters at specific positions. A famous example used by German agents during WWII: "Apparently neutral's protest is thoroughly discounted and ignored. Isman hard hit. Blockade issue affects pretext for embargo on by products, ejecting suets and vegetable oils." Reading only the second letter of every word: "Pershing sails from NY June 1." The surrounding text was meaningless filler; the message was hidden in the pattern.
Since the 1980s, most color laser printers have secretly embedded a pattern of tiny yellow dots on every printed page. The dots are nearly invisible — arranged in a precise grid, they encode the printer's serial number, the date, and the time of printing. The EFF (Electronic Frontier Foundation) discovered and documented this system in 2005 after decoding the patterns on pages from multiple printer manufacturers. The dots exist at the request of governments for document forensics — tracking counterfeit currency, for instance. Most people have no idea their printer is silently watermarking everything they print. We've written a full article on printer tracking dots if you want to go deeper on this one.
Digital steganography emerged as images moved onto the internet. Copyright holders began embedding invisible watermarks into images and audio files — identifiers that survive copying, resizing, and moderate compression. Today, digital watermarking is standard practice in stock photography, film distribution, and document tracking. When a leaked movie gets traced back to a specific screener copy, it's usually because of an imperceptible watermark embedded in the video.
Digital image steganography using LSB (Least Significant Bit) encoding is the modern version of all of these techniques — hiding data in pixel values that are imperceptible to the human eye. If you want to understand how it works at a technical level, our steganography explainer covers the method in detail.
Try LSB image steganography yourself — encode a secret message into a PNG and extract it later. Runs entirely in your browser with no uploads.
Open Steganography Tool