Validation doesn’t work without JS

Hello,

First, thanks for this plugin !

Sadly, the validation process doesn’t seem to work when I disable JavaScript.
After looking at the source code (securimage-wp.php), it seems that this condition fail:

...
} elseif (!isset($_POST[$tid]) || $_POST[$tid] != siwp_get_token($captchaId)) {
...

$_POST[$tid] seems to be empty when JavaScript is disabled.

I tested this with Safari on Mac OSX.

Thanks for your help.