What does your contract with your website developer say, did they warrant that they had not violated the rights of anyone in constructing your site? If they did warrant that (or something similar), they breached that warranty, by violating the rights of the photographers who Getty represents by misappropriating their photos.
First, ask Getty to verify the rights of the photographers by sending you copies of the copyrights of the photos. If the copyrights are valid, take the photos down. Then consult a lawyer to review your contract with your website developer and see if you can work out a settlement with the website developer and Getty.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
You can read a number of responses when this issue was addressed before. See http://bit.ly/6TYef5
In addition, Attorney Oscar Michelen has developed a niche practice assisting clients in this area. See http://extortionletterinfo.com/
These are the answers to this question -- there's nothing more to be said, except to warn anyone who published a website and may be reading this about how important it is to nail down exactly where the images you're using came from, and under what circumstances.
Daniel, thanks for the link to Oscar Michelen!