Removing width and height attributes from

I don’t remember where I found this. It works for me, almost…

add_filter( 'post_thumbnail_html', 'remove_thumbnail_dimensions', 10 );
	add_filter( 'image_send_to_editor', 'remove_thumbnail_dimensions', 10 );

	function remove_thumbnail_dimensions( $html ) {
		$html = preg_replace( '/(width|height)=\"\d*\"\s/', "", $html );
		return $html;
	}

But, when I add a caption to an image it does not work. The height/width attributes gets added to <img>.
Suggestions?