If you’re not using properly licensed images and/or photos you could be subject to a lawsuit. Typically most marketers do not know which images they can use legally. While Google images is a great resource, for the most part you cannot legally use any of those images which are returned in a search.
If you are in need of good quality stock photography you should either purchase them through a stock photo site such as ThinkStockPhotos.com, iStockPhoto.com, etc. Or alternatively you could use an open source stock photography site.
Below is a list of free public domain stock photography sites:
Creative Commons Photo Search Tool - Search for open source images from all of the web’s top resources (Google, Flickr, Wikipedia, etc.)
Every Stock Photo – This is a search engine of free photos. But be careful, not all are free for commercial use. Be sure to read the individual license on each photo before using.
Flickr Creative Commons Search – This is one of the best places to search for photos, but you need to read the licenses for each photo to see what it can be used for legally.
Free Digital Photos - Download free premium stock photos and illustrations.
Free Media Goo - Here are some royalty free photos, background images, and textures.
Free Pixels – Over 5000 free stock photos/images that can mostly be used for commercial use.
Free Range Stock - A collection of high resolution photos submitted by various photographers that can be used in just about any commercial projects.
FreeStockPhotos.com – Free photography for commercial or personal use.
Historical Stock Photos – A collection of old public domain photos of historical figures.
Morgue File – Great resource for finding high resolution stock photos for illustrations or design needs. All of the images are completely free for personal or commercial use.
Open Clipart – A repository of public domain clip-art images.
Open Stock Photography – Stock photos released under wikimedia creative commons licensing.
Pixabay – Find high quality stock photos without any limitations.
Pixel Perfect Digital - Creative commons licensing of images without any limitations (some attribution may be required).
Public Domain Photos – This site features more than 5000 free photos and 8000 free clip-art files that can be used for both personal and commercial use.
Public Domain Pictures – Repository of free public domain images. Most are free for commercial use.
Stock Photos for Free – Over 100,000 images come with a royalty free license so that they can be used in all types of media (including commercial).
The Stock.XCHNG - A great resource for free stock photos. Be sure to read the individual licensing terms for each image before use. Most do not require any sort of attribution.
USA Government Public Domain Photo Index – Most of the images will be either public domain or US government works which can be used without permission.
Wikimedia Commons Search – Over 17 million freely usable media file. Some photos may require attribution. Restrictions may apply.