makefile.php

<?php
if (isset($GLOBALS["HTTP_RAW_POST_DATA"])) {
    // Get the data
    $imageData = $GLOBALS['HTTP_RAW_POST_DATA'];

    // Remove the headers (data:,) part. 
    // A real application should use them according to needs such as to check image type
    $filteredData = substr($imageData, strpos($imageData, ",") + 1);

    // Need to decode before saving since the data we received is already base64 encoded
    $unencodedData = base64_decode($filteredData);

    // Save file.  This example uses a hard coded filename for testing,
    // but a real application can specify filename in POST variable
    //$fp = fopen("images/genimg".date("YmdHis").".png", 'w');
    $fp = fopen("images/img_" . microtime(1) . ".png", 'wb');
    fwrite($fp, $unencodedData);
    fclose($fp);
}