Forum Moderators: open
But there's an even easier way for a visitor to your site to disable scripts
You could perhaps display a transparent GIF over your image to render it unclickable, without relying on script. But then if you're using CSS then that could also be disabled.
As lavazza suggests, it's rarely worth the effort - particularly since a screen grab is just a press of the print screen key!
If you are bothered about copyright, then you could think about watermarking the images - although this might obviously ruin them.
If it's social networking, then your users have to be aware that anything they post is available to all - unless you give your users control over who can view them.