(PHP 5 >= 5.5.0, PHP 7)
imagecropauto — Crop an image automatically using one of the available modes
$image
   [, int $mode = -1
   [, float $threshold = .5
   [, int $color = -1
  ]]] )
This function is currently not documented; only its argument list is available.
imageAn image resource, returned by one of the image creation functions, such as imagecreatetruecolor().
mode
      One of IMG_CROP_* constants.
     
threshold
      Used in IMG_CROP_THRESHOLD mode.
     
color
      Used in IMG_CROP_THRESHOLD mode.
     
   Return cropped image resource on success or FALSE on failure.