$image['tmp_name']  = "/tmp/unnamed.png";
$image['file_image']    = base64_encode(file_get_contents("/tmp/unnamed.png"));
$image['name']      = "unnamed.png";
$image['file_name'] = "unnamed.png";
$image['type']      = "image/png";
$image['submit'] = "UPLOAD";

$url = 'http://localhost/api/upload_image';

$postdata = http_build_query(
    array(
        'file_name' => 'form variable1',
        'file_image' => file_get_contents($image['tmp_name'])
    )
);

$opts = array('http' =>
    array(
        'method'  => 'POST',
        'header' => 'Content-Type: multipart/form-data',
        'content' => $postdata
    )
);

$context  = stream_context_create($opts);

var_export(file_get_contents($url, false, $context));

class UploadImage(webapp.RequestHandler):
    def post(self):
        img         = Images()
        img.image   = self.request.get('file_image')
        img.name    = self.request.get('file_name') or "no name"
        img.put()

        self.response.headers.add_header('content-type', 'application/json', charset='utf-8')
        self.response.out.write('{"status": "OK", "image": "'+img.key.urlsafe()+'"}')