As instructional designers, we are always looking for new and bigger collections of freely available image and educational resources to use when developing courses. According to Merriam-Webster, images in the public domain "belong to the community at large, are unprotected by copyright or patent, and are subject to appropriation by anyone." In other words, they can generally be utilized by anyone in virtually any situation for educational, personal, or commercial projects. As such, these are the types of images we seek in order to be free of copyright restrictions and legal liabilities. Most designers have their favorite image galleries to peruse, but I would like to share what I have found to be one of the largest collections of public domain image resources available:
Lunch Time, Economy Glass Works, Morgantown, W. Va.October 1908.
Image from The Library of Congress, part of "Photographs from the records of the National Child Labor Committee (U.S.) 2004667950" -- found by searching The Flickr Commons at https://www.flickr.com/commons. Direct link to this image on Flickr: https://flic.kr/p/d2yDf1.
Getty images has made the decision to open some of its works, both public domain and some to which Getty holds the rights, to be released "freely, for any use" - starting with works from the Getty Museum's collection.
So far they've released just shy of 5000 high quality public domain images,
with an intent for this to grow. You can read more about this on the The Getty Iris, or you can jump right to the Getty search portal (I've taken the liberty of specifying the Open Content Images for your perusal). Links below.
For some it will be old news, but Flickr has a section called The Commons, filled with photos believed to be in the public domain. Here's one of the repository's most recent additions, a 1952 photo of "Santa Claus handing out treats to nine young women on the beach."
Holiday hijinks aside, the repository boasts the participation of a wide assortment of international libraries, museums, and institutions, all attempting to make photos believed to be in the public domain available to the public. The Flickr community is asked to help tag photos with information so that it becomes a usefully searchable archive. If you're looking for photos for an online course or other project it would be worth a closer look.
Here's a sampling of the sorts of images available, any of which can be clicked to visit the image's page on Flickr: