It looks as if the theme specifically calls for gravatar.
Do you get the same behavior if you paste the following code into your child theme functions.php file? (do so carefully, and preferably through FTP and not the WordPress dashboard)
function evolve_comment_avatar( $avatar = true, $gravatar_size = 45 ) {
global $comment;
$author = get_comment_author();
if ( $avatar ) {
// Get author's gavatar
$gravatar_email = get_comment_author_email();
$gravatar_size = apply_filters( 'evolve_gravatar_size', (int) $gravatar_size ); // Available filter: evolve_gravatar_size
$gravatar = get_avatar( $comment, $gravatar_size );
// get the $src data from $gavatar
if ( preg_match( '/src=\'(.*?)\'/i', $gravatar, $matches ) )
$src = $matches[1];
// Rebuild Gravatar link because get_avatar() produces invalid code :/ (P.S. adds "gravatar" class)
$output = "<img class=\"avatar gravatar gravatar-{$gravatar_size}\" alt=\"{$author}'s Gravatar\" src=\"{$src}\" width=\"{$gravatar_size}\" height=\"{$gravatar_size}\" />";
if (get_option('show_avatars')){ // Avatars enabled?
return apply_filters( 'evolve_comment_avatar', (string) $output ); // Available filter: evolve_comment_avatar
}
}
}
That slightly modifies the method for retrieving the image. Let me know.