You can definitely cite figures and diagrams from published papers.
Kindly see two examples below on how you could cite figures and diagrams (also remember to add the full citation in your reference list or bibliography).
Also, see a link affixed below for more information on this topic. All the best!
Thanks. This article says we need to have a copy right permission. Some authors don't reply to email and if the figure on the Internet site, it is hard to get permission.