If you want to quickly hide a file inside an image, then nothing beats FireSteg add-on for Firefox. This plugin allows you to both hide and extract any important file from a jpeg, png, and bmp image instantly.
Once you have installed this add-on, go to View > Sidebar and select FireSteg. Now select the file that you want to hide and the image in which you want to hide. Note that both the file and image can be selected from either local drive or directly from any web page.
Once it is hidden, by default the image will be saved on your desktop. You can always change the location by going to Settings tab.
To extract the file from an image that resides on the local drive, go to Extract tab, select the image, and click Extract.
If someone sends you an image with a hidden file inside it via email or any other method, you don’t need to download the image first. Simply right-click the image and select Add To FireSteg(file to extract), this will extract the hidden file from the image to your desktop directly.
The whole process of adding and extracting an important file from an image has been made easier with this add-on. You don’t need to write complicated command lines, nor you will ever need a 3rd party tool. And yes, it encrypts the file before hiding it inside an image.
Download FireSteg Firefox Add-on