Code:
RewriteEngine on
RewriteCond %{HTTP_REFERER} ^http://google.com/images [NC]
RewriteRule .* http://xxxtremeblog.com/redir/extremesponsor.php [NC,L]
for google images it should be like this.
but remember its only for .com, you will need to do some regex to get all google domains incase they come from google.ru etc.