Glad you asked this question. So many folks just assume that the photos posted here are just there for the taking.
The customary and legal way to obtain a copy of a published/copyrighted photograph is to ask the photographer for permission. Most of us will gladly give permission for usage.
My personal policy is that if it is for profit use, magazine, advertisement or corporate use then I will ask for some payment.
If it is for non-profit informational or personal use then I will grant permission free of charge.
You can contact the photographers on this site by clicking on the "contact " link under the photo in the "photo information" area.
Thanks again for doing the right thing and asking !!