There are thousands of free image files available for you on the Web to download and use to illustrate your website, blog, articles, etc. There are even those that you can put onto zazzle or other print-on-demand products and sell.
But if you do not understand the different categories of copyright and free images, you may inadvertently use a photo or clip-art image in a way that violates the rights of the artist. With all the material that is freely available, there is no reason to exploit the work of others nor to put yourself at risk of costly lawsuits.
You will find here definitions of copyright categories so that you can immediately understand when you see the type of license under which an image was published. I will also provide the URLs for websites that. list image resources and those that explain the licenses in greater detail.