Go to Myportablesoftware website download the portable app.
Once the download has completed, extract it.
A donation screen will appear, click on the skip donation button to launch the application.
On the right hand side check the box to allow you to use a custom password to encrypt the file with, and type in a password.
Hit the large camouflage button to start hiding your files.
Now when you look at the file in explorer, you will see that it has a much bigger file size but the new file will still open like an ordinary image. The size that the file increases by will obviously vary depending on what you are hiding.
To get your file back, switch to the de-camouflage tab, select your picture, remember to check the box and input the same password you used to encrypt the file. If you use the wrong password your file will not be able to be decrypted, and you will get an error message like so.
However if you supply the right password, your files will be extracted to the directory that you specified.
Besides the obvious increase on file size there is no way that anyone would be able to tell that there was any hidden contents in the image.