[php]
add_filter( ‘post_thumbnail_html’, ‘remove_width_attribute’, 10 );
add_filter( ‘image_send_to_editor’, ‘remove_width_attribute’, 10 );

function remove_width_attribute( $html ) {
$html = preg_replace( ‘/(width|height)="d*"s/’, "", $html );
return $html;
}
[/php]