If you can't find Public Domain images that fit your needs, you can also use Creative Commons-licensed content. The sources below make finding these images, and properly attributing them, quick and easy.
As with Google, not all images available via Bing's image search are available under a Creative Commons license. However, once you run a search using Bing Images, you can limit your results to appropriately licensed images by clicking on "License" in the menu below the search box. Though users are not able to limit by specific types of Creative Commons licenses, there are definitions of their categories to help you match the license to your needs. You can also limit by Public Domain images.
Compfight is another tool that shows both commercial and Creative Commons images, but it sets off the non-Creative Commons images in a separate section to make the distinction clear. Once you have run a search, you also have various facets in the left menu that can help you narrow your results by license type (along with other features of the image)
Europeana is an online collection of content from European libraries, archives, museums and other institutions. Once you run a search in their search bar, you can limit your results to items that are freely usable or available under a Creative Commons license using the facets under Copyright in the left menu.
This section of Flickr offers images that are available under a Creative Commons license and also explains the different types of Creative Commons licenses. You can also search for Creative Commons-licensed images on Flickr by going to the advanced search link in the upper right hand corner of the page and checking the appropriate boxes in the Creative Commons section at the bottom of the advanced search page. You can upload your photos to Flickr and choose to offer some or all of them under a Creative Commons license.
This is another tool for finding Creative Commons images on Flickr. It allows you to save images you are interested in and either view them on Flickr or download them and also provides information on proper attribution.
While not all images on Google Images are Creative Commons licensed, it is possible to limit your search results to only images available under a Creative Commons license. To do so, run your search in the standard Google Image search bar and then on the results page, click on search tools just below the search box. A further drop down menu will then appear with usage rights as one of the options. From there, users can limit results to the proper rights. Unfortunately, they do not use the exact language of Creative Commons licenses, but you can nevertheless use the service to find usable images.
The images on this website are all by Ryan McGuire and have all been released from copyright restrictions using Creative Commons 0 (or CC0). This means that they have been dedicated to "open, public domain," but this is not synonymous with the legal concept of the public domain. It does, however, mean that these images can be used without attribution. While there is no way to search for a specific type of image, you can browse easily and the images are all freely available for high resolution download.
This tool from TinEye allows you to search for Creative Commons-licensed images by color. Users can enter up to five colors simultaneously and will return dozens of images that include all of the selected colors. Images are pulled from Flickr.
This image search engine returns both Creative Commons and non-Creative Commons images. When you download any image, you can also download the necessary HTML to appropriately attribute the image to its creator.
This website collects stock images that are focused on start up companies. While you cannot search for specific subjects, browsing through the images is simple. All of the images are licensed under a CC BY license.
All photos published on Unsplash are licensed under Creative Commons Zero which means you can copy, modify, distribute and use the photos for free, including commercial purposes, without asking permission from or providing attribution to the photographer or Unsplash.
This site offers fully searchable access to media, including images, sounds and videos, that has been uploaded by users, mostly for use on Wikipedia. Most of the content is available under some sort of Creative Commons license and licensing information is clearly provided at the bottom of each piece of media's individual page.