SharePoint Mythbusting: The response header contains the current SharePoint version http://www.wictorwilen.se/sharepoint-mythbusting-the-response-header-contains-the-current-sharepoint-version

get_sharepoint_version.php

<?php

function getSharePointVersion($url)
{
	$headers = array();

	$raw_headers = get_headers($url);

	foreach($raw_headers as $index => $raw_header)
	{
		if($index > 0)
		{
			list($name, $value) = explode(": ", $raw_header, 2);

			if($name === "MicrosoftSharePointTeamServices")
			{
				return $value;
			}
		}
	}

	return "UNKNOWN";
}

$url = "http://sharepoint_site_url/";

echo getSharePointVersion($url);

?>