$re = '/;center=([.\d]+)%?[0-9A-Z]+([-.\d+]+)/';
$str = '<img alt="Map" height="135" src="http://maps.google.com/maps/api/staticmap?scale=2&center=45.504358%2C-73.553712&language=en&zoom=15&markers=scale%3A2%7Cshadow%3Afalse%7Cicon%3Ahttp%3A%2F%2Fyelp-images.s3.amazonaws.com%2Fassets%2Fmap-markers%2Fannotation_64x86.png%7C45.504358%2C-73.553712&client=gme-yelp&sensor=false&size=286x135&signature=nM1FwS0L3z_VgK2ljaRcJf11HxA=" width="286">';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php