$re = '/[a-f\d\-]+ # Matches a-f, any digit, - (hyphen)
# ^ One or more times (+)
\/ # Matches a /
.+ # Matches any character one or more times
\. # Matches a . (dot)
(?i) # States that anything after this is case-insesitive
# ^ Inline Flag
(jpg|jpeg|gif|png) # Selects file extension
# ^ (either jpg, jpeg, gif, or png)
(?-i) # Removes Inline Flag/x';
$str = '"/stories/main_imagescache/20160319-1549-2202-5826/blueapronimage.jpg';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($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