//提取图片路径src的正则表达式，$content图片路径所在的html，$matches提取的数据
   preg_match_all("/<img(.*)src=\"([^\"]+)\"[^>]+>/isU", $content, $matches);
 
    $desImg = $patterns = [];
    if (!empty($matches)) {
        //取值，地址路径在第三个
        $desImg = $matches[2];
    }
            
    if (!empty($desImg)) {
        //过滤重复值
        $desImageList = array_unique($desImg);
        foreach ($desImageList as $img) {
            $imgNew = "/" . preg_replace("/\//i", "\/", $img) . "/";
            $patterns[] = $imgNew;
        }
     }
               
     //替换图片路径，$patterns，当前图片路径，$newImg新的图片路径
     $newDescription = preg_replace($patterns, $newImg, $content);