Steganography, you know? No, here's a definition from Wikipedia:
Steganography is the art of concealment: its purpose is to convey a message unnoticed in another message. It differs from cryptography, the "art of secrecy," which seeks to make a message unintelligible to anyone other than who-of-right. To take a metaphor, steganography would consist of burying one's money in one's garden where cryptography would consist of locking it in a safe — that said, nothing prevents the two techniques from being combined, just as one can bury a safe in his garden. http://fr.wikipedia.org/wiki/St%C3%A9ganographie
And of course, steganography exists in computer science, especially since everything is virtual: You only see what you want to see! Take this image, for example: Is
there a difference with this one? 
no? And yet, there is a text file hidden in one of the 2 images! And if you download both images to your computer, you'll see that both images have the same weight!
How to hide a folder in an image
First, I'll explain how to hide compressed files in an image:
- Take a picture, and convert it into a GIF image. To do this, no matter the image editing software will do the trick. Let's take the simplest, the one built into Windows, that is Paint!
- So you open your image with Paint, then you do "Save in Image in GIF format"
Be aware that converting the image into GIF may give a lower quality image, but hey, the goal is to hide files in an image, so the quality doesn't matter.
- Save your GIF image in a folder at the base of your hard drive, for example in a folder called stegano
- Create your files that you want to hide in the image. Select these and make a right click, Send to, Compressed Folder
(You can create your compressed folders with compression software like 7-Zip, Winrar, Winzip, etc. This way you can add a password!)
- Make sure all your files (image – compressed folder to hide) are in the same stegano folder
- Make sure your files and folders don't have space in their names
- Open a Windows control line: click the Windows button, tap cmd and press your Entry button
or
- Windows Menu, All Programs, Accessories, Order Line
- Type cd 'stegano' (stegano being the name of the folder where you put all your files)
- Then type copy /B NameDeImage.gif-NomDuDossierACacher.zip NameDeImageFinaleWanted.gif (Replace by the names of your files: NameDeImage.gif being the image, NameDuDossierACacher.zip being the compressed folder and NameDeFinaleDeM.gif the name that will be applied to your new shorthand image)
And lo and behold, your new image is created, with your hidden files in it!
How to access the folder hidden in an image
To retrieve your steganographed folder, it's pretty easy:
- Click right on your image, Open with, choose your compression program like 7-zip, Winrar, Winzip and others
or
- Open your compression software, navigate up your image as you will from your Windows Explorer, double click on your image, and hop magic, you'll have access to your folder if cleverly hidden!
There are of course software specialized in shorthand, but this trick has the advantage of not using any! There you go! Now that you have all the cards in hand, tell me, what is the image that hid a top secret file? ;-)