$re = '/<img\s+[^>]*\bsrc="[^"]*\/signature\.gif[^\>]*\>/m';
$str = '<img src="http://example.com/someimage1.jpeg">
<img src="http://example.com/someimage2.jpeg">
<img src="http://test.mydomain.com/project433q325/track/Images/signature.gif">
<img src="http://example.com/someimage4.jpeg">
<img style="OVERFLOW: hidden; WIDTH: 0px; MAX-HEIGHT: 0px" alt="" src="http://test.mydomain.com/project433q325/track/Images/signature.gif?id=446&etc=1586624376">
';
preg_match_all($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