Do the author accounts on this site have a Gravatar set for their email addresses? Gravatar pulls in the image that’s been uploaded and associated with a specific email address. So, when a user on a WordPress site uses that email address in their profile, it gets automatically displayed in notifications, author widgets, and the like.

If there’s a Gravatar already assigned for the email address in use on the site, and it’s not displaying properly, it may be that the theme is not calling in the Gravatar properly. You can troubleshoot this by temporarily changing to one of the WordPress default themes, such as Twenty Twenty.

When you’re using Twenty Twenty, if the Gravatar properly shows, you’d need to contact your theme’s developer and let them know the theme doesn’t appear to be pulling in your Gravatars properly.

Does this help?