$img_data = $_POST['data'];
$id = $_POST['id'];
$type= $_POST['type'];
session_start();
$_SESSION['chart-image-'.$id] = $img_data;
define('UPLOAD_DIR', 'graph'); //'Graph means your folder name'
$base64img = str_replace('data:image/png;base64,', '', $img_data);
$data = base64_decode($base64img);
if($type!=='')
{
$file = UPLOAD_DIR .'/'.$id.'-'.$type.'.png';  
file_put_contents($file, $data);    
}
$review_file = UPLOAD_DIR .'/review-graph-'.$id.'.png';   
file_put_contents($review_file, $data);