Both Morguefile and Pixaby offer free stock photos, many of which don't require any attribution at all. Flickr's Creative Commons section is also an excellent resource for anyone searching for royalty-free photos, whether for commercial or personal use.
Most browsers allow you to download any image on the Internet, but it isn't always legal to do so. It's important to check all photos for licensing requirements before you download them. This is true whether you plan to use the photo for personal or commercial use.
Free use photos are totally free and do not require any attribution. Legally, you may use these in any fashion you see fit without penalty, even if your goal is to resell them or use them in commercial developments. You can also remix them, use them in art projects, sell them on your website, or use them in business marketing materials.
Creative Commons guidelines use a six-tiered licensing categorization system. The most common application, called Attribution, designates that anyone may use the image as long as they credit the artist.
Attribution-ShareAlike carries the additional requirement that any derivative works must also use Attribution licensing. Attribution-NoDerivs allows anyone to share, use or pass on the images, but indicates that you may not use the images to create derivative works. Attribution-NonCommercial-ShareAlike and Attribution-NonCommercial-NoDerivs both follow the same guidelines, but prevent any commericial use.
Photos with Attribution-NonCommercial licensing are essentially free for use with attribution, but you may not use them commercially.