$re = '/(<[\s]*(?![\/])figure.*?>)|(([^<.*figure.*>\w])(<[\s]*(?![\/])img.*?>)([^<.*\/*figure.*>]))/mi';
$str = 'аываыва <img sdasd asd > sdf dsf < sdf imG>
<h2>
< H2 sdf > </h2> sdf sdf sdf sdfsdf sdf sd f
< sdf sdf H2 sdf >
</h2>
< h2> adasd asd < h2>
< / H2>
<img 2>
<figure><img></figure> ыва ыва ыва ыва ыва ыва
< figure >< img >< / figure >
< figure sdfsdfsdfsd f> asd as das asd< img asd asd a/> asd asd asd <> < / figure> фываы ва ыв
<img>
< figure > фыв ыфв фыв фыв ыфв < img > < / figure >
<figure itemprop="associatedMedia image" itemscope="" itemtype="https://schema.org/ImageObject"> <meta itemprop="representativeOfPage" content="true"> <img itemprop="contentUrl url" src="//site.com/url.jpg" title="" alt=""> <meta itemprop="name" content=""> <meta itemprop="width" content=""> <meta itemprop="height" content=""></figure>';
preg_match_all($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