Avatars are popular as identification and with the service Gravatar it is largely used in the comment area of different applications.
WordPress allows the user some basic settings. For example loading a default or generated Avatar, if the commentator doesn't have one.
Various themes have a standard Avatar to match the design. But even here there is a nice solution via a hook, which enables to add an avatar in the list of your backend to make a selection quite simple. In the following I would like to show with a short and simple code snippet how to add 2 new avatars to the array of WordPress.

You have to add this little function to functions.php of your theme and it will add 2 Avatar from your folder images of your theme directory. I suggest, that the Avatars have a size of 60 pixel.

/**
 * add a default-gravatar to options
 */
if ( !function_exists('fb_addgravatar') ) {
	function fb_addgravatar( $avatar_defaults ) {
		$myavatar = get_bloginfo('template_directory') . '/images/avatar.gif';
		$avatar_defaults[$myavatar] = 'people';

		$myavatar2 = get_bloginfo('template_directory') . '/images/myavatar.png';
		$avatar_defaults[$myavatar2] = 'wpengineer.com';

		return $avatar_defaults;
	}

	add_filter( 'avatar_defaults', 'fb_addgravatar' );
}

Is the theme active, you will have the 2 new Avatars available in your list.