$re = '/(?<=src=)"[^" ]*\/(?=[^\/"]*\/)/';
$str = '<img width="594" height="392" src="/sites/it_kb/SiteAssets/Pages/exploding%20the%20VDI%20vDesktop/VDI3.PNG" alt="" style="margin:5px;width:619px;height:232px" />';
$subst = "";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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