php - get image from base64 string

Question

I am trying to take a base64 encoded string and return it as an image in php using $_POST. On line one if I use $_POST['imgdata'] it returns error from the preg_match if i were hard code the base64 string instead of using $_POST it all works and returns the image. how can i make this work by using the $_POST

works

$imgstr = 'data:image/png;base64,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';

does not work

$imgstr = $_POST['imgdata'];

full code

$imgstr = $_POST['imgdata'];   
// Grab the MIME type and the data with a regex for convenience
if (!preg_match('/data:([^;]*);base64,(.*)/', $imgstr, $matches)) {
    die("error");
}

// Decode the data
$content = base64_decode($matches[2]);

// Output the correct HTTP headers (may add more if you require them)
header('Content-Type: '.$matches[1]);
header('Content-Length: '.strlen($content));

// Output the actual image data
echo $content;

Answer 1

As was noted the "+" should not be missed, the rest is straight forward. Use $_REQUEST if you are not sure is it post or get.

// requires php5
define('UPLOAD_DIR', 'images/');
$img = $_REQUEST['img'];
$img = str_replace('data:image/png;base64,', '', $img);
$img = str_replace(' ', '+', $img);
$data = base64_decode($img);
$file = UPLOAD_DIR . uniqid() . '.png';
$success = file_put_contents($file, $data);
print $success ? $file : 'Unable to save the file.';