cidExists example

$data = base64_decode($match[3]);
                    } elseif ('' === $match[2]) {
                        $data = rawurldecode($match[3]);
                    } else {
                        //Not recognised so leave it alone                         continue;
                    }
                    //Hash the decoded data, not the URL, so that the same data-URI image used in multiple places                     //will only be embedded once, even if it used a different encoding                     $cid = substr(hash('sha256', $data), 0, 32) . '@phpmailer.0'; //RFC2392 S 2
                    if (!$this->cidExists($cid)) {
                        $this->addStringEmbeddedImage(
                            $data,
                            $cid,
                            'embed' . $imgindex,
                            static::ENCODING_BASE64,
                            $match[1]
                        );
                    }
                    $message = str_replace(
                        $images[0][$imgindex],
                        $images[1][$imgindex] . '="cid:' . $cid . '"',