Question

The code below is modified from an O’Reilly Book – Learning PHP, MySQL, and JavaScript which can be found here

Why are all image types converted to .jpg?

Does .jpg offer the best quality/size ratio?

  public static function upload()
    {    
    $email=$_SESSION['email'];
    $path1="i8.jpg";
    $path2="z_p/$email.jpg";
    $path3="i9.jpg";     
    $path4="z_p/$email-1.jpg";     
    if(move_uploaded_file($_FILES['ufile']['tmp_name'], $path2))
      {
      $typeok=TRUE;
      switch($_FILES['ufile']['type'])
        {
        case "image/gif":   
          $src = imagecreatefromgif($path2); 
          break;
        case "image/jpeg":  
        case "image/pjpeg": 
          $src = imagecreatefromjpeg($path2); 
          break;
        case "image/png":   
          $src = imagecreatefrompng($path2); 
          break;
        default:            
          $typeok = FALSE; 
          break;
        }  
      if($typeok)
        {
        list($w, $h) = getimagesize($path2);

        $tw  = $w;
        $th  = $h;

        /*Run 1*/

        $max = 50;
        if($w > $h && $max < $w)
          {
          $th = $max / $w * $h; 
          $tw = $max;
          }  
        elseif ($h > $w && $max < $h)
          {
          $tw = $max / $h * $w; 
          $th = $max;
          } 
        elseif ($max < $w)
          {
          $tw = $th = $max;
          } 
        $dst = imagecreatetruecolor($tw, $th);
        imagecopyresampled($dst, $src, 0, 0, 0, 0, $tw, $th, $w, $h);           
        imagejpeg($dst, $path2);
        imagedestroy($dst); 

        /* Rune 2 */

        $max = 20;
        if($w > $h && $max < $w)    
          {
          $th = $max / $w * $h; 
          $tw = $max;
          }  
        elseif ($h > $w && $max < $h)
          {
          $tw = $max / $h * $w;     
          $th = $max;
          } 
        elseif ($max < $w)
          {
          $tw = $th = $max;
          }
        $dst = imagecreatetruecolor($tw, $th);
        imagecopyresampled($dst, $src, 0, 0, 0, 0, $tw, $th, $w, $h);       
        imagejpeg($dst, $path4);
        imagedestroy($dst);
        imagedestroy($src);
        }
      }
    else
      {
      copy($path1, $path2);
      copy($path3, $path4);
      }
    }

Answer 1

There are lots of nasty surprises you can hide inside a jpeg file (or any of a number of image formats). By always recreating an image this way, you gain a certain amount of confidence that the image your server issues is sanitized.