If you have come across a photograph that you love and think that it would be great for your own use online, you must have permission and know where it came from.  If you get it from a random website and the photographers information isn't there, that doesn't mean it's up for grabs, so don't think that they wont come after you for using the photograph on your own website.  Just because you like a picture and you can right-click and save, doesn't mean you should.  Always make sure that you know the origin and that you have permission.  Or better yet, hire a Pro to take some pictures for you.  Otherwise, It can turn into a huge legal hassle and possibly hundreds of thousands of dollars.