How to hide multiple types of information in the same file?
One simple steganographic technique is to just use the comment structure of a mark-up language to embed plaintext messages. For example, the html code
&lt;!-- ATTACK AT DAWN --&gt;
&lt;img src=&quot;lolcat.jpg&quot;&gt;

inserted in a web page and opened in a browser will render as an image (presumably of an amusing cat), but if opened in a text editor the comment line can be read (and the cat picture can not be examined).
In particular the jpg format allows COM segments which are preceded by the bytes 0xFF 0xFE and a length field which then allow insertion of ASCII text.
Note that this is pretty trivial to detect and provides only steganographic protection (vice cryptographic).