Unless a signed contract between photographer and subject says otherwise, then all pictures by a photographer are automatically copyrighted to the photographer (in the US anyways). Use of those pictures would depend on the particular contract (ie; commercial, personal, portfolio, advertisement etc). Posting on the internet is considered 'publishing' to my knowledge.

Here's a good site of semi pro, wanna be pro, and actual pro photographers on a message board forum. There's weeks worth of reading there for suggestions, advice, etc. from the business end of photography. There's alot more to it than many people think.
http://community.mpix.com/forums/16.aspx