The Visual Media office at Luther College manages a PhotoShelter account in which all of their recent and past photographs are available for viewing and download. All of the photographs uploaded to the Visual Media PhotoShelter account can be used for any Luther College website.
To download an image, first click on the image you want to download, then click on the down arrow in the bottom right corner. Go ahead and click the blue button that says "Download", select the option "Save File", then OK.
Wikimedia Commons contains a wide collection of public domain images, which allows for their free use on other websites.
Many of the images on Wikimedia Commons are released under a Creative Commons license that allows for their free use on websites. Authors of the images may require that attribution is provided.
HowlingPixel.com lets you view Wikipedia pages as photo galleries. Just enter your search term at the top of the page.
PhotoShelter's advanced search option allows for filtering search results based on keywords, date range, and image location.