Totally not a good idea to use photos from Google images. Most of them are subject to copyright and the penalties for infringement can be severe. We've had a digital photography business for the last ten years or so and people stealing images has been a nightmare. Really glad I'm winding that down these days.
Best is to use your own images and if this is not possible, as Alan mentioned use Creative Commons photos. They are all over the place - a big Commons section on Flikr for example. Make sure that you if you use any CC images, you stick to what the licence requires.
Some are licensed as non-commercial so you can use them on a personal blog but not a business one. Others are fine for business as long as you provide attibrution to the licence holder.
Personally, I think CC is the best way to go (I have several sites that are licensed CC) - you can read more on the licenses and the requirements at the link in Alan's response.
Edit - a quick thought, just this week we bought licenses for some images for a tradeshow backdrop at http://www.shutterstock.com/ Very reasonably priced and huge selection.