6 ms·

The author claims it is possible to detect an image having some possible data. How does one detect this?

• dexterdog 4y ago
  usually by the fact that a 200x200 jpg is 15MB
• Retr0id 4y ago
  The LSBs of a typical photograph are not uniformly random. For example, here's the blue channel LSBs of the input image from the repo: https://i.imgur.com/lOVlcpU.png https://i.imgur.com/lOVlcpU.png If they are uniformly random, then you know something is up.
  • ale42 4y ago
    This image is clearly showing JPEG artifacts, you'd never see such square blocks in an photograph that has not been compressed with a lossy algorithm.
    • bawolff 4y ago
      JPEG is super common. Having jpeg compression artifacts, even in images that have been converted to a different format, is not something that will raise eyebrows.
    • Retr0id 4y ago
      I should have clarified, I'm not talking about the JPEG artifacts, I'm talking about everything else. The faint outlines of objects you can see, the varying textures, and the areas of clipping (where the source-brightness was either above 255 or below 0). There are other statistical correlations not visible in that image - correlations between the different channels, and between the different bits within a channel. If I showed you the most significant bit of some non-JPEG'd image, you could obviously see that it's non-random (since it'd essentially be a threshold function). If I showed you the second-most significant bit, it would again be non-random, but perhaps less obviously so. As you go through the bits, it starts looking more and more random, but there are still going to be statistical tests you can do to distinguish from true uniform random bits.