- var_dump: documentation ( source)
- preg_match: documentation ( source)
<?php
$regex='#^(<[^>]+>)*<img#i';
var_dump(preg_match($regex,'<p><span><a href=""><img src="some.jpg"></a></span></p>'));
var_dump(preg_match($regex,'<p>Text text text<span><a href=""><img src="some.jpg"></a></span></p>'));
var_dump(preg_match($regex,'<p><span>Text text text<a href=""><img src="some.jpg"></a></span></p>'));