You need to extract the base64 image data from that string, decode it and then you can save it to disk, you don’t need GD since it already is a png.
$data="data:image/png;base64,AAAFBfj42Pj4";
list($type, $data) = explode(';', $data);
list(, $data) = explode(',', $data);
$data = base64_decode($data);
file_put_contents('/tmp/image.png', $data);
And as a one-liner:
$data = base64_decode(preg_replace('#^data:image/\w+;base64,#i', '', $data));
An efficient method for extracting, decoding, and checking for errors is:
if (preg_match('/^data:image\/(\w+);base64,/', $data, $type)) {
$data = substr($data, strpos($data, ',') + 1);
$type = strtolower($type[1]); // jpg, png, gif
if (!in_array($type, [ 'jpg', 'jpeg', 'gif', 'png' ])) {
throw new \Exception('invalid image type');
}
$data = str_replace( ' ', '+', $data );
$data = base64_decode($data);
if ($data === false) {
throw new \Exception('base64_decode failed');
}
} else {
throw new \Exception('did not match data URI with image data');
}
file_put_contents("img.{$type}", $data);