Q: All the things I'm using images of are really old, so I don't have to worry about copyright, right?
A: Unfortunately you may have to worry about copyright, especially for images.
The four factors of "fair use" are:
Works created in 1925 or earlier are typically in the public domain, which means they can be used and repurposed in many more ways.However, keep in mind that even if you are using a picture of something that is thousands of years old, the copyright applies to the *picture* and not the thing the picture is of (meaning a picture of the Parthenon is unlikely to be in the public domain unless you know it was taken with an early camera).
Often, it is okay to use images if you are using them for classroom use only. But if you are presenting or publishing your work, you need to think through copyright much more carefully.
And no matter the source type, even if it is public domain, when working in an academic realm, remember you need to cite it!
Individuals are widely responsible for not only finding the images used in their published works but also for securing copyright permission to use them. Here is the Library & IT guide to copyright information along with other copyright information.
Here are the online collections of some of the biggest museums that provide public domain images of some of their collections, if the work itself is in the public domain (or assumed to be in the public domain if the creator is unknown).
Remember that for many of these collections, there are copyrighted images as well. Many of these sites provide search tools or indicators of if an image is in the public domain. Want to be sure? Reach out to your librarian for support navigating these sites!