When searching for OERs, please note that in addition to the material being available freely online, it must be shared with a licence permitting the reuse in the way you intend to use it (i.e. just using the content as it is or adapting it). In addition, consider the quality of the source and the accessibility of the content to your intended audience.
Europeana (cultural heritage image collections and stories)
Wikimedia Commons (always check the licence information at the bottom of the page)
Google advanced search (under the ‘Usage rights’ section, select either ‘free to use or share’ or ‘free to use share or modify’ depending on how you would like to use the resource)
Flickr (select the ‘Commercial use & mods allowed’ from the drop down ‘Licence’ menu when searching)
Pixabay (images, illustrations, vector graphics, videos, music, and sound effects)