Steganography is the art and science of writing hidden messages in such a way that no one, apart from the sender and intended recipient, even suspects the existence of a hidden message. Steganography has been in use since at least 440 BC when Demaratus sent a secret message by writing it directly on the wooden backing of a wax tablet before applying its beeswax surface. Creative uses have been to tattoo a slave's head or brand a sheep - then wait for the hair/wool to grow back before sending the message to the recipient. "Invisible Ink" made popular in TV spy shows was actually used since the first World War. In WWII a "hum" heard in the background of an innocent radio transmission might be recorded, then slowed down to reveal that it is actually Morse code looping a message. You can also "blink" in Morse code as evidenced by videos made of American POWs during the war in Vietnam.
Invisible Ink is still in use!
These days, the Information Super-Highway fills in for the sheep-paths and palm-top tablets have replaced the wax ones but the game remains the same. Data can be embedded into even a modestly sized image and sent by email, linked on Geocaching.com or used as a forum avatar without anyone ever being suspicious. This is possible because of the enormous amount of data contained in a picture.
Sometimes the first letter of the pop-up text on a row of images is used too.
A relatively small image - just 1024x768 in screen real estate - consists of 786,432 pixels. If the image is true-color, each pixel contains 24 bits of color information. This is distributed evenly with 1 byte allocated to Red, Blue and Green. This allows for 256 different values for each color for a total of over 16.7 million colors for each pixel. If we wanted to hide some information in the bits of this image we would have 18,874,368 opportunities. If this was a fancy new digital camera with a 24 megapixel sensor than we're looking at over half a billion distinct bits of information in which we can hide a message.
So how, within all that information, could we even hide a message? Let us deconstruct the image into a few pixels. They look like this: ... Three little pixels all in a row. Not much of an image but this is just the start. Imagine they are all black. That means they have no color information and they will have all zeros for their red, blue and green values. A data byte is made up of 8 bits and each bit is a binary 1 or 0. This makes our first three pixels full of zero color look like this:
How very uninteresting. The naked eye can't see the difference between the thousands of potential shades between white and black so the naked eye wouldn't even perceive the difference between that and this:
In this example we changed the least significant bit of the colors. The difference in the colors would be impossible to notice. But, with the power of a computer, a pattern might be easily derived. Break up the string into chunks of 8 bits and transpose them to visualize what is happening.
px1 00000000 red
px2 00000001 red
px3 00000001 red
So we add a little color to the first pixel's green values. The second pixel gets a bit more red. The third pixel gets more red and blue color. As illustrated, looking at just the last digit of the strings, we've changed the third, fourth, seventh and eighth instances of the least significant bit. Taking those 8 bits in a row you get 00110011. Converting from binary to the familiar base 10 we get 51 which just happens to be the ASCII code for the number 3. In this tiny three-pixel image we managed to encode a secret number invisible to the human eye. Imagine what you could do with millions of pixels?
Imagine what you could do with a full cache page?
Of course, not every set of three pixels would contain encrypted data - that probably would change the image visibly. There is usually a key to show which bytes to remove for analysis of hidden data. This key is can come in any form - including other images - so this method of encryption can be extremely complicated and extremely secure.
Unfortunately, all of this is still pretty hard to grasp and doesn't make a very good geo-puzzle for a few reasons:
1) You would need to be a computer to analyze every pixel of an image looking for patterns.
2) The Image itself is likely to be chock-full of nearly useless information besides the message.
3) You need access to The Key to decrypt the patterns in The Image. The key is most likely scrambled too. A puzzle within a puzzle.
4) Puzzles requiring Digital Steganalysis (IE: 3rd party software) are frowned upon by Geocaching.com.
5) This whole thing is a gross over-simplification that would get me stoned in crypto circles. Ain't no one got time for that!
To discover the hidden message contained in this cache, you will need to find both The Image and The Key. Correct use of The Key is... well, the key to success. Once your key is operational the coordinates will line up and jump through hoops for the mighty keymaster. Because of rule 4 mentioned above, this is a physical example of a message encoded using Steganography. No software required! Hardware will be required however but only the kind of things you keep in your stationary drawer and/or sewing kit.
Assuming a printer fits in your drawer or sewing kit.
You can check your results by interrogating the No-Frills-Geochecker.
This cache is certified Central Jersey!