get_attrs.php

<?php
$html = '<img class="medium" src="/images/image.jpg" width="100" height="75">';

// get attrs
preg_match_all('~([\w]+?)="(.*?)"~i', $html, $m);
$attrs = array_combine($m[1], $m[2]);

print_r($attrs);

// result
/* 
Array
(
    [class] => medium
    [src] => /images/image.jpg
    [width] => 100
    [height] => 75
)
*/