How to remove hard coded dimensions from post gallery images?

How can I insert pictures into a post without any hard coded dimensions (e.g. <img src="" alt=""/ > instead of <img src="" alt="" width="" height="" />)? I’m using this snippet, but it doesn’t seem to work properly with images pulled via wp_get_attachment_image();:

`function remove_img_src($html) {
    $html = preg_replace('@(width|height)="([0-9])+" ?@i', '', $html);
    return $html;
}

add_filter('image_send_to_editor', 'remove_img_src', 10, 8);
`
Any ideas?