In an ideal world, there would be one central place to search for all openly-licensed content. The Mason OER Metafinder, OASIS, MERLOT, OERCommons, LibreTexts, and Google Advanced Search all aim at being comprehensive, so it can be hard to know where to start. Of all these, I like OERCommons because it has many useful search criteria to increase relevancy. Before diving into these large pools of resources, though, I first see if there's anything relevant in two more curated collections:
There are also many discipline-specific OER sites (including SkillsCommons for CTE), as well as institution or state-specific sites like Open Oregon State and BCCampus.
If you're not finding appropriate resources for certain topics or objectives, talk to a librarian! As you work, it's important to keep track of potential sources. Here's a spreadsheet template from Michele DeSilva at COCC that you can use to do that.
You will find many openly-licensed images within the OER above. But here are some other places I often look for images, specifically:
If you find a freely available online resource that is under "all rights reserved" copyright (and, remember, this probably applies to any resource that isn't in the public domain or openly licensed), it's generally okay to link to it, since a link is essentially a reference to the resource. YouTube's terms of service even enable you to embed videos from the platform in your course materials, as you have seen me do throughout this course (just don't share links to pirated copies of materials. If you're not sure if a link goes to a legal copy, check with a librarian).