[This tip is for information purposes only. Always use technology for good intensions. ]
Take any JPG file and place inside a folder. Place the files to hide inside same folder and zip the altogether to a single file (do zip even if there is only one file to hide)
Open terminal and switch to the folder where you put those files
catfilestohide.zip >> myimage.jpg
This command will attach the zip file at the bottom of the jpg file. You can check the size of new jpg file, it will be increased.You can simply delete your filestohide.zip file because it is added inside the image.
Click open the jpg file in any image reader app, you can see the same old image, and no information about the file you added inside.
To retrieve the file back rename the jpg file to .zip extension.
Form terminal type unzip myimage.zip , this will show some error/warning in zip file format, but you can get the filetohide.zip file unzipped in same folder.
[In Windows, if Winzip not work, use 7zip to unzip compressed hidden files]