It is not a good idea to copy images that you find on Google search.  Many of these images are copyrighted.  You can be sued for a lot of money if you use an image without permission.

Here is a list of some of the more common sources for free images.  They do not all use the same license, so check it out before copying, but generally, these places allow you to copy, edit, change, and display without restrictions.

This list is not in any particular order: