Copyright issues of using free clipart I'm a master student in psychology. A year ago, I downloaded a lot of free clipart online to create my study stimuli. For example, some clipart are from this website: http://clipart-library.com. 
I basically created my study stimuli using clipart from multiple sources. I finished writing up my thesis and plan to publish it soon. However, it occurs to me that if I publish my study with a few figures of experimental stimuli, it may incur copy right issues. I'm wondering what would be the best option for me at this moment? Should I not include any figures in my publications?
The terms of use page of the site in your link says "All images on our site are for Non-Commercial Use," which should include academic use.  If you include any of their figures, give appropriate credit.  For material from other sites, read their terms of service and give the required credit.

In any case, be sparing in using clip-art in a thesis.