est.
 * @return bool True if suitable, false if not suitable.
 */
function file_is_displayable_image($path) {
	$info = @getimagesize($path);
	if ( empty($info) )
		$result = false;
	elseif ( !in_array($info[2], array(IMAGETYPE_GIF, IMAGETYPE_JPEG, IMAGETYPE_PNG)) )	// only gif, jpeg and png images can reliably be displayed
		$result = false;
	else
		$result = true;

	return apply_filters('file_is_displayable_image', $result, $path);
}

?>
XML-RPC server accepts POST requests only.