In WordPress you can assign avatars to your authors, but if you have avatars then you need to be able to use them.
In this snippet you will see how you can display the author avatar in the post display.
Wordpress has a built in function
<?php echo get_avatar( $id_or_email, $size, $default, $alt ); ?>
You will use this to display the author avatar, by using the following snippet.
<?php echo get_avatar( get_the_author_email(), '128', '/images/no_images.jpg', get_the_author() ); ?>