You can hide files inside images.
For example, if you have an image “myimage.jpg” and have a file “mysecretfile.rar”, you can combine the zip file with image, so most people only see it as just an image.
To do this, go to DOS prompt, then type the command
copy /b myimage.jpg + mysecretfile.rar new_image.jpg
Now you will get a new image file with name “new_image.jpg”.
To get the data, just rename it to “new_image.rar”, now you will be able to open the file using WinRAR and extract the data in the RAR file.