Choose a challenge from the Cops thread, determine the third hidden message, and describe how the system works.

Keep in mind limitations and possibilities available to Cops:

  • You are not expected to guess any cryptographic secrets or additional information required to extract the hidden messages, as they should have already been included in their post.
  • The hidden message will be in English
  • The hidden message may be encoded as plain text, a text bitmap rendering, audio clip, or ascii art font. This encoding will be consistent across all hidden messages.
  • No further processing will be required after obtaining the hidden message.
  • Data is allowed to be hidden in metadata, but at least one bit of one pixel must have been used for something.

Score 1 point per cracked system.


2 Answers 2



I don't know the first thing about image encodings, but it looks like in each of the three images every pixel is an index into a palette containing two identical colors. Messages are encoded as transposed images in the palette indices.

Thus, the third image says STEGANOGRAPHY:

enter image description here

  • 1
    \$\begingroup\$ Correct ! it can also be viewed by changing one of the colors of the palette in GIMP (or equivalent) (window > Dockable Dialogs > Colormaps) \$\endgroup\$
    – CreaZyp154
    Commented Dec 21, 2021 at 13:00

emanresu A's

Image 1, which encodes HI, can be decoded by turning it into a 32×32 square:

The word "HI"

Same with Image 2, which encodes BYE:

The word "BYE"

And, with Image 3:

The words "OI You!"

The words OI You!

Since all the images are 1024×1, you just need to split it into segments 32 pixels wide, and stack them on top of one another.

Here's a tool I wrote to do this: https://gist.github.com/Radvylf/b5d1bc5f39903400b243abf2041feefe


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