I know there has been many threads here that deals with taking down illegal images or sites that give out free images. Can someone explain or point out to a thread that explains this process in detail?
Is contacting google the only way to go?

thanks lisa. looks like an uphill battle for the contributors.

First step after attempting to contact the site's owners would be to issue their web hosting provider (you can get this from the whois records) with DMCA takedown notice, most hosting companies will comply if it's a legitimate copyright infringement and take the site offline. If the site is hosted by a reseller you then have to search their whois records and find out who hosts them and do the same.

Also if they have google adsense ads on the site you can issue google with a DMCA, google will usually block their ads loosing them revenue.