Wrap container div to inside div

I am having an issue with this page https://academicperspective.com/staff/.

Each author has a div for their author box (class=”author”). Within the box, there is a div with the class “avatar” into which a piece of PHP code outputs the appropriate image. If you look at the page now, you will notice the first box looks perfect. However, in the second two, to which no content has been added, the image extends outside of the containing “author” div. How, either in CSS or by changing my HTML, can I make the “author” div expand to fit the image, if it is the largest object, as it does the text?