You must run these examples from a web server. file:// won't work. Sadface.
http://pngdrive.devinhaus.com/examples/decode.html
http://pngdrive.devinhaus.com/examples/decode_steganography.html
http://pngdrive.devinhaus.com/examples/encode_file_drag_drop.html
http://pngdrive.devinhaus.com/examples/encode_file_select.html