The author of a book who adds a contributor needs to upload an image for the contributor.

They can do that by editing an existing contributor on the contributors page for each book (or when they set up the contributor initially) by going to the Contributors page for their book:

...making sure to replace YOUR_BOOK with their book's unique web address.

We understand people might expect their profile image to show up here on their contributor profile, but this feature was made to be specifically configurable in each case where a contributor is added..