2 min read

A Cipher Based on Similar Pictures

After I finished the computational photography on the coursera, I finally know some basic principles about the digital pictures. The peer-viewed assignment which focused on the epsilon photography is very interesting. In fact, I know nothing about this term before but when I take some photos, I found it awesome to perform something interesting. Recently, Google plus showed a new feature named auto awesome, which is a good application of epsilon photography; but I want to talk about using similar photos to hide some information.


  • Digital photos are made using pixels which look like a matrix of cells;
  • Each cells might have 3 numbers which stand for Red, Green, Blue(yes, RGB color model), for a UINT-8 format photos, each numbers stand for the intensity of corresponding color: 0 for totally black, 255 for totally white;
  • Our PCs or Macs relay on the numbers to display the right color for us;
  • Similar photos usually show most of the pixels same with few changed or most of the pixels changed with the same patterns, so their differences could be used to hide information.


  • For similar photos, you could get 3 channels to calculate the differences;
  • The differences could get by a derivation of corresponding pixels by rows or columns;
  • Differences must have the same meaning in a UINT-8 so you will get a differences plot;
  • Well, you could use this to plot the words you want.


Form and content are in fact the same thing, all you need to do is that finding a meaning for each. Maybe they could show in the same way. Everything could be given a meaning when you find one which could be approved by others. But I don’t think it is a good idea to give all the phenomenon a tag or meaning, it is silly and meaningless. Life is not easy and we need no more troubles on purpose. Anyway, I just like to use the patterns which could have different meanings on different points of views to make up something and it is really awesome.


Well, I have written what I want to say and the conclusion is the impression in your mind right now.


  • GEB: you must know I have read this, isn’t it?
  • Computational Photography: this class is from GA Tech if you want to know the details of what I said.
  • Cipher: this game will teach you a lot.