圖片品質前後對比 ： var_dump(exif_read_data($img));檢視 ，嚴重失真壓縮比為 50%。

壓縮前：

array (size=18)
  'FileName' =>  '1367000585017724053.JPG' (length=23)
  'FileDateTime' =>  1367029384
  'FileSize' =>  67872
  'FileType' =>  2
  'MimeType' =>  'image/jpeg' (length=10)
  'SectionsFound' =>  'ANY_TAG, IFD0, THUMBNAIL, EXIF'
 
 (length=30)
  'COMPUTED' => 
    array (size=7)
      'html' =>  'width="300" height="300"' (length=24)
      'Height' =>  300
      'Width' =>  300
      'IsColor' =>  1
      'ByteOrderMotorola' =>  1
      'Thumbnail.FileType' =>  2
      'Thumbnail.MimeType' =>  'image/jpeg' (length=10)
 

  'Orientation' =>  1
  'XResolution' =>  '72/1' (length=4)
  'YResolution' =>  '72/1' (length=4)
  'ResolutionUnit' =>  2
  'Software' =>  'Adobe Photoshop CS Windows' (length=26)
  'DateTime' =>  '2013:04:26 10:56:18' (length=19)
  'Exif_IFD_Pointer' =>  164
  'THUMBNAIL' => 
    array
 
 (size=6)
      'Compression' =>  6
      'XResolution' =>  '72/1' (length=4)
      'YResolution' =>  '72/1' (length=4)
      'ResolutionUnit' =>  2
      'JPEGInterchangeFormat' =>  302
      'JPEGInterchangeFormatLength' =>  5519
  'ColorSpace' =>  1
  'ExifImageWidth' =>  300
  'ExifImageLength' =>  300

壓縮之後：

array (size=8)
  'FileName' =>  '1367000585108300044.jpg' (length=23)
  'FileDateTime' =>  1367029385
  'FileSize' =>  38802
  'FileType' =>  2
  'MimeType' =>  'image/jpeg' (length=10)
  'SectionsFound' =>  'COMMENT' (length=7)
  'COMPUTED' => 
    array (size=4)
      'html' =>  'width="300" height="300"' (length=24)
      'Height' =>  300
      'Width' =>  300
      'IsColor' =>  1
  'COMMENT' => 
    array (size=1)
      0 =>  'CREATOR: gd-jpeg v1.0 (using IJG JPEG v62), quality = 100
' (length=58)

<?php
$img_thumb  = imagecreatetruecolor($thumb_width, $thumb_height);
$bgcolor = trim($bgcolor,"#");
sscanf($bgcolor, "%2x%2x%2x", $red, $green, $blue);
$clr = imagecolorallocate($img_thumb, $red, $green, $blue);
imagefilledrectangle($img_thumb, 0, 0, $thumb_width, $thumb_height, $clr);
imagecopyresampled($img_thumb, $img_org, $dst_x, $dst_y, 0, 0, $lessen_width, $lessen_height, $org_info[0], $org_info[1]);

圖片只要經過那個函式的壓縮，仍舊是失真的，圖片檔案大小壓縮率為 50%。