Unfortunately there is no way to copy proof a screen with ANY
technology. A message recipient can always store an unencrypted
version.
You can prevent newbies from using copy in the browswer, with a java
script, but any experienced user will know th somply turn-off java
support in the browser to get around it.
You can convert text to an image, but they can take a screen capture
to save the image.
There's simply no way to prevent it.
Lance