Although you can find icons and clip art with the all-purpose image search engines, these image types all have their own specialized engines, which is why I put them in their own category. Please keep in mind that most materials that you will find with these search tools are copyright protected, and that you should ask for permission before you use them.
Image Search Engines
Flickr advanced search: https://www.flickr.com/search/advanced/(opens in new window)
Google https://images.google.com/(opens in new window)
https://images.search.yahoo.com/(opens in new window)
US Govt Photos and Images https://search.usa.gov/search/images?affiliate=usagov&query(opens in new window)
PicFindr(opens in new window) "searches the web for stock photos that are completely free to use commercially. It is a web app that helps you search several stock image, public domain and photo ommunity sites simultaneously."
Picsearch.com(opens in new window) According to their web site, picsearch "has a relevancy unrivalled on the web due to it's patent-pending indexing algorithms. Also, Picsearch has a family friendliness that allows children to surf in safety as all offensive material is filtered out by our advanced filtering systems."
TinEye(opens in new window) Reverse Image Search
Every Stock Photo(opens in new window) Searches multiple sites for free photos
Icon/Clip Art Search Tools
The Icon Browser(opens in new window) (In Knight (1998) Also referred to in Media Builder. MetaLab, University of North Carolina
Iconfinder(opens in new window) Monthly rates to use
More Specialized, Subject Area Engines
Artcyclopedia(opens in new window) "The fine art search engine."
Public Health Image Library(opens in new window) "PHIL is an extensive collection of still images, image sets, and multimedia files related to public health." Most of the images in the collection are in the public domain and are thus free of any copyright restrictions, but see the PHIL site for conditions of use.
Permission must be obtained for non-public domain images
You are responsible for obeying copyright laws and any conditions stated on the sites that you access.