<?
$im = imagecreatefrompng("img.png");
$w = imagesx($im);
$h = imagesy($im);

$break = false;
for ( $i = 1; $i < $h; $i++ ) {
  if ( $break ) break;
  for ( $j = 1; $j < $w; $j++ ) {
    $color = imagecolorat($im, $j, $i);
    if ( $color !== 2147483647 ) {
      $break = true;
      break;
    }
  }
}
$up_line = $i;

$break = false;
for ( $i = $h - 1; $i > 0; $i-- ) {
  if ( $break ) break;
  for ( $j = $w - 1; $j > 0; $j-- ) {
    $color = imagecolorat($im, $j, $i);
    if ( $color !== 2147483647 ) {
      $break = true;
      break;
    }
  }
}
$bottom_line = $i + 1;

$break = false;
for ( $i = 1; $i < $w; $i++ ) {
  if ( $break ) break;
  for ( $j = 1; $j < $h; $j++ ) {
    $color = imagecolorat($im, $i, $j);
    if ( $color !== 2147483647 ) {
      $break = true;
      break;
    }
  }
}
$left_column = $i;

$break = false;
for ( $i = $w - 1; $i > 0; $i-- ) {
  if ( $break ) break;
  for ( $j = $h - 1; $j > 0; $j-- ) {
    $color = imagecolorat($im, $i, $j);
    if ( $color !== 2147483647 ) {
      $break = true;
      break;
    }
  }
}
$right_column = $i + 1;

$new_h = $bottom_line - $up_line;
$new_w = $right_column - $left_column;

$new = imagecreatetruecolor($new_w, $new_h);
imagefill($new, 0, 0, imagecolorallocatealpha($new, 0xFF, 0xFF, 0xFF, 127));
imagesavealpha($new, true);

imagecopy($new, $im, 0, 0, $left_column, $up_line, $new_w, $new_h);

header("Content-Type: image/png");
imagepng($new);