EDIT

Missread, Sorry.

Its impossible to "STOP" copying/downloading images from a website, but there are many things you can do to make it harder.

Disable right click (javascript)
Use CSS and place the images as "background-url" (CSS)
Password protect, or place a blank index.html page in the images folder

Hope these helped a little.

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(this will stop people from using the images on THEIR website.)

You need to have hotlink protection.

Here is a good result I found from google:

http://altlab.com/htaccess_tutorial.html

If your not familiar with a scripting language, I would suggest doing this manually (or batch it), before upload.

If you have PHP GD2 I think theres quite a few methods you could use to make it a bit more dynamic for instance - http://ditio.net/2007/07/11/creating-watermarks-with-php-and-gd-library/

Thanks Willr

Dumb question, but what is GD?

I have had a look at the link you listed but I still don't know whether I have GD as part of Silverstripe or whether it is an extra download and install.

Cna you please let me know what GD stands for

Many thanks