How to Embed Hidden Messages in Picture Files (OS X)

Yes, just like in the movie Along Came a Spider, you too can hide messages inside of jpg, gif, png and other picture files.

Please note: iSteg, the software used in this guide, is no longer in development and does not work in modern versions of macOS. It’s listed as supported in: OSX 10.5-10.8, but it also says that it works in OS X versions above 10.8 – it’s just not clear at which version of OS X it stops working. It absolutely does not work in macOS 11 “Big Sur”. If you’re using an older version of OS X, give it a shot – it’s a small download.

  1. First up, download and install iSteg. The installation is a breeze – just unzip the file, open the .dmg and drag iSteg to your Applications folder. Launch it from there.
  2. Enter a password in the Password: field. This is the password that the person receiving your encrypted picture will need to know in order to extract the hidden message.

  3. click to enlarge

  4. Click the plus (+) button next to the Source Picture File field, and navigate to the picture you want to hide a message in. Select it and click the Choose button.
  5. Open your favorite text editor and write out the message you want to send/embed in the picture. Save the file.
  6. Back in iSteg, click the plus (+) button next to the Source Text File field. Navigate to the text file you just created and saved, select it, and click the Choose button.

  7. click to enlarge

  8. Click the Process button. Give a name to the output file and select a location to save it. Click Save.
  9. iSteg will do its thing, and you’ll be presented with a summary window. Click the Close button.

  10. click to enlarge

  11. Now send your picture (the output one) to whomever you wanted to share your secret message with. They too will need to use iSteg to retrieve the hidden message (or outguess 2.0, or another app that is a front-end for outguess 2.0).
  12. When they have the file, they’ll need to enter the same password in the Password: field, and select that file using the Source Picture File button. But this time, they’ll have to remove the check mark from the Encode: field.

  13. click to enlarge

  14. Then click Process to decrypt the file. If the password is correct, they’ll be asked to give the output file a name, and a location to save it.
  15. iSteg will once again do its thing, and this time a summary window of the decoding process will be displayed.

  16. click to enlarge

  17. When they open the file that iSteg created, it will contain your secret hidden message.

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