No, I hate to burst your bubble, but these are not free images. If you intend on selling your projects, please go to a reputable source for clip art and royalty-free stock photography. Many of the images that you will find through Google's search are indeed copyrighted or otherwise owned.
Google just finds images out there on the net. They are indexed by file name and by the alt tag info.
Just be careful what you pull, especially if you are going to use it for something for sale - you could get slapped with a copyright infringement lawsuit or at the very least a "cease and desist."
There is a lot of good info in this craftster thread regarding images and copyright: Copyright Info / Using Other Peoples' Images / Etc