<?php

$images = <<<END
<img src="/data/img/201108031_023" width="300" height="400" />
<img src="/data/img/201108031_026" width="250" height="300" />
<img src="/data/img/201108031_028" width="400" height="300" />
<img src="/data/img/201108031_032" width="500" height="400" />
...
END;

preg_match_all("/<img[^>]*width=\"([3-9][0-9]{2}|[1-9][0-9]{3,})\"[^>]*>/",$images,$matches);
print_r($matches);

?>