Are there any databases of materials that I can use for free without worrying about copyright?

Yes. There is a wealth of material out there which is either in the public domain (meaning copyright has expired) or available under Creative Commons licensing, which generally means the work is available for free, subject to certain limited conditions, such as non-commercial use only and acknowledgment of the author. This includes open access publications, which generally use Creative Commons licenses.

For Creative Commons materials, visit the Creative Commons website for more information and search their Openverse. Content in the Wikimedia Commons is almost entirely Creative Commons-licensed. Google Images has a filter (under "Tools" > "Usage Rights") to select Creative Commons-licensed results only (note: you should always check the content's original site to confirm its license), and content sites like Flickr and YouTube also have such filters.

For public domain material, simply search online for ‘public domain’ and the type of material you’re interested in. Some useful sites include: Project Gutenberg (the largest collection of copyright-free books online) and Wikipedia, which has an entire page dedicated to public domain resources. 

For other online materials, a recommended best practice is to check the website’s "Terms of Use" or "Legal Notices" section to confirm what conditions apply to use of the website’s material. In some cases, you may be able to use the material for free for non-commercial and educational purposes.

SFU Library also subscribes to a number of image databases. These contents can typically be used for teaching and learning purposes.