Blocking Access from All but a specified domain

[Lord_Override]

I need to stop all but one site from linking to images, exactly like what xoom does but moreso, if it is possible I'd like to be able to stop anyone accessing them (even if they type in the exact url) unless they are from that specific domain. I don't mean user hostnames I mean a web site. I'll give an example. If I have site http://www.y.com with the image file on it, and I only want to be able to have the image seen if it is accessed from site http://www.z.com (as in a file on z.com has an image tag to it in its files.)
If I'll clarify.
An image on site A can only be accessed if its linked to from Site B.
Is this possible? If it is, would I be able to do it with apache on its own or would I need to make a cgi script of some sort to check the page that the request for the image is coming from?
Thanks You.

[freebsd]

Start here -> ftp://ftp.ccs.neu.edu/pub/mirrors/Apache/dist/httpd/contrib/modules/1.2/mod_block.c
if DSO is available. If you don't know how to add module to Apache,then start here -> http://httpd.apache.org/docs/misc/rewriteguide.html and check for Blocked Inline-Images.

If you are having trouble with Apache, go to -> http://forums.devshed.com/ and check out the Apache forum instead.

[Lord_Override]

Thanks a lot.

[The King Ant]

This might be helpful: http://apachetoday.com/news_story.php3?ltsn=2000-06-14-002-01-PS