php下载图片到本地，图片打不开,该怎么处理

php下载图片到本地，图片打不开
环境：wampserveer
数据库编码：统一utf8_general_ci
php文件编码:utf-8
该函数不与数据库连接时,下载正常
我用php上传统一图片后再下载就无法打开
我怀疑是上传到mysql后文件编码问题,但从未涉及这一方面,小弟特此求教如何解决

PHP code

<!--

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-->function dl_file($file){
     //这是下载文件的函数,$file是文件路径.
    //First, see if the file exists
    if (!is_file($file)) { die("<b>404 File not found!</b>"); }

    //Gather relevent info about file
    $len = filesize($file);
    $filename = basename($file);
    $file_extension = strtolower(substr(strrchr($filename,"."),1));

    //This will set the Content-Type to the appropriate setting for the file
    switch( $file_extension ) {
          case "pdf": $ctype="application/pdf"; break;
      case "exe": $ctype="application/octet-stream"; break;
      case "zip": $ctype="application/zip"; break;
      case "doc": $ctype="application/msword"; break;
      case "xls": $ctype="application/vnd.ms-excel"; break;
      case "ppt": $ctype="application/vnd.ms-powerpoint"; break;
      case "gif": $ctype="image/gif"; break;
      case "png": $ctype="image/png"; break;
      case "jpeg":
      case "jpg": $ctype="image/jpg"; break;
      case "mp3": $ctype="audio/mpeg"; break;
      case "wav": $ctype="audio/x-wav"; break;
      case "mpeg":
      case "mpg":
      case "mpe": $ctype="video/mpeg"; break;
      case "mov": $ctype="video/quicktime"; break;
      case "avi": $ctype="video/x-msvideo"; break;

      //The following are for extensions that shouldn't be downloaded (sensitive stuff, like php files)
      case "php":
      case "htm":
      case "html":
      case "txt": die("<b>Cannot be used for ". $file_extension ." files!</b>"); break;

      default: $ctype="application/force-download";
    }

    //Begin writing headers
    header("Pragma: public");
    header("Expires: 0");
    header("Cache-Control: must-rev alidate, post-check=0, pre-check=0");
    header("Cache-Control: public"); 
    header("Content-Description: File Transfer");
    
    //Use the switch-generated Content-Type
    header("Content-Type: $ctype");

    //Force the download
    $header="Content-Disposition: attachment; filename=".$filename.";";
    header($header);
    header("Content-Transfer-Encoding: binary");
    header("Content-Length: ".$len);
    @readfile($file);
    exit;
}

1、检查传入参数 $file 内容是否正常
2、检查所有参与的文件是否有 bom 头
------解决方案--------------------
获取扩展名，建议用pathinfo

------解决方案--------------------

一定是数据库编码的问题，因为你都说了不用数据库时正常，
再访问数据库时，SET Names utf-8;
所有格式统一；
建议检查图片文件名称，大小，看是不是个正常文件，确定图片没以二进制存在数据库中
图片在服务端是否正常，传输过程是否被加密
------解决方案--------------------
首先对照一下异常的图片和正常的图片，有什么区别，然后再寻找异常原因才是正解吧...

如果异常图片只是开头或结尾被破坏，那就是php代码本身写的有问题，哪里截断或添加了异常数据；
如果图片整体内容都被破坏了，那基本就是编码问题

另外...图片放数据库里？ 凌乱了...