<?php
$content = <<<FIM
text text text text <img src="path/to/image/1">text text text text
<img src="path/to/image/2">
text text text text text text text text text text text text text text text text <img src="path/to/image/3"><img src$
<img src="path/to/image/5">
FIM;
$frst_image = preg_match_all( '|<img.*?src=[\'"](.*?)[\'"].*?>|i', $content, $matches );
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