You may consider to use filters (see the FAQ), for 
example:

-* +www.mydomain.com/*.html +www.mydomain.com/*.gif 
+www.mydomain.com/*.jpg +www.mydomain.com/*.png

Or also, if you want all images on xxx.mydomain.com:

-* +www.mydomain.com/*.html +*mydomain.com/*.gif 
+*mydomain.com/*.jpg +*mydomain.com/*.png

You can also accept all gif, like in:

+*.gif