Getting applets to work is not for the faint of heart and it gets harder and harder as time goes on.  This is too bad because it is a great way to use DStretch.  
If you find solutions to applet problems please email me (DStretch@prodigy.net).

Some issues I have found:

On Windows (and maybe Macs) Java 8 requires that you add http://www.DStretch.com to the exceptions site list in the security tab of the Java Control Panel.
If you are using Java 7 you need to set the security level to medium in the Java Control Panel.
On some Macs Safari seems to be unable to load applets. 
On some Macs Firefox can hang when doing DStretch enhancements.  My guess is that this is due to having an old version of Java.  Try to get the latest version.

If you want to use the applet on your own files you may need to increase applet memory.  See the first applet page for more help on this subject.

Launch ImageJ DStretch
                Applet
Click on the image to open an ImageJ applet with DStretch plugin.  The applet
can open sample images from many different rock art sites.

El dDpugon Applet
                site
Click on the image to see my photos from Cueva El Dipugon.  You can
use the DStretch ImageJ applet to enhance the colorful paintings yourself.