There is a patchwork of state rules governing the design of firm web sites and the use of imagery in advertising. Here are some informative links on this topic.
ABA Marketing Ethics Link:
http://practice.findlaw.com/law-firm-marketing/law-firm-marketing-ethics/
ABA Lawyer Advertising Rules by State:
http://www.abanet.org/legalservices/clientdevelopment/adrules/
FindLaw White Paper: The Ethics of Online Client Development:
http://practice.findlaw.com/law-practice-management-articles/lawyermaketing-ethics-whitepaper.pdf