$re = '/<img [^<]*(height:[ \d]+px;?)[^>]*>/';
$str = '<div style="height: 300px"><img style="color:red;" src="#"><aaa style="height:400px"><img src="t.jpg" title="ā" style="width:1000px; height: 300px"><img src="t.jpg" style="width:1000px; height: 500px"><eee src="t.jpg" style="width:1000px; height: 500px"><img alt="ķķ" src="#" style="height:2450px; visibility:hidden"/>';
preg_match_all($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