I am working on a startup that provides information services, kind of like dating website but for legal community.
I wonder what kind of disclaimers are needed for pictures that show people giving their opinion about site services. Like what linkedin has on their front page except users are not real. Right now I just put small text on the pic stating that this is commercial advertisement and that results may be different for other people. I basically took disclaimer that I saw during infomercial on TV. Does anyone have good resource where I can read up on this?
You don't necessarily need a lawyer, but you need to KTL : Know The Law
First, check out the FTC disclosure requirements for your type of service: http://www.ftc.gov/os/2009/10/091005endorsementguidesfnnotice.pdf (for a shorter read: http://blog.rafflecopter.com/2012/07/ftc-blogger-guidelines/ )
Also, lawyers have some extra rules related to advertising. It's not clear from the question if they would apply to you or not but this article might be helpful: http://www.totalattorneys.com/attorney-marketing/state-by-state-cases-and-the-new-landscape-of-lawyer-advertising/
As long as you have made it clear that it is an advertisement and not a representation of your customers you will be fine. But what is considered clear is somewhat subjective.
Your customers should be legal professionals, so you may want to ask one of them :)