Try this I know this will only allow the sites you want to access it. I know it will be able to let you view pics but I cant figure out why it wont allow mpegs to download. But this code should work for just letting certain sites in and getting pics. Maybe someone can modify the code to all asf and mpegs to be downlaoded also.
AuthUserFile /dev/null
AuthGroupFile /dev/null
RewriteEngine On
RewriteCond %{HTTP_REFERER} !^
http://www.site-a.com [NC]
RewriteCond %{HTTP_REFERER} !^
http://site-a.com.com [NC]
RewriteCond %{HTTP_REFERER} !^
http://www.site-b.com [NC]
RewriteCond %{HTTP_REFERER} !^
http://site-b.com [NC]
RewriteRule /*
http://redirect-them-somewhere.com [R,L]
Hope that helps