How to add php to theme to show alt attributes

Try adding these codes to your theme’s function.php file:

function isa_add_img_title( $attr, $attachment = null ) {

    $img_title = trim( strip_tags( $attachment->post_title ) );

    $attr['title'] = $img_title;
    $attr['alt'] = $img_title;

    return $attr;
}
add_filter( 'wp_get_attachment_image_attributes','isa_add_img_title', 10, 2 );