Checking failed CAPTCHAs...?

[StepOnFrog]

Looking at the vB register template, there is a conditional <if> as the tempalte loads, that checks to see if any errors occured during a previous registration attempt...

PHP Code:

<if condition="$show['errors']">
 <table class="tborder" cellpadding="$stylevar[cellpadding]" cellspacing="$stylevar[cellspacing]" border="0" width="100%" align="center">
 <tr>
  <td class="tcat">$vbphrase[errors_occurred_during_registration]</td>
 </tr>
 <tr>
  <td class="alt1"><ul>$errorlist</ul></td>
 </tr>
 </table>
 <br />
</if> 


How can I use, or can I use the $vbphrase[errors_occurred_during_registration] to check which type of error occured on the registration form?

Specifically, I want to check whether the CAPTCHA was failed during registration.

Thanks in advance,
step