SetEnvIfNoCase Referer "^http://www.mathmistakes.info/" locally_linked=1
SetEnvIfNoCase Referer "^http://www.mathmistakes.info$" locally_linked=1
SetEnvIfNoCase Referer "^http://mathmistakes.info/" locally_linked=1
SetEnvIfNoCase Referer "^http://mathmistakes.info$" locally_linked=1
SetEnvIfNoCase Referer "^$" locally_linked=1
<FilesMatch "\.(gif|png|jpe?g)$">
  Order Allow,Deny
  Allow from env=locally_linked
</FilesMatch>