Hi,
If you want to display the recaptcha plugin under a custom address field, you can change the line:
$components = array('view' => array('checkout','user'),'viewvar' => 'ctrl', 'lengthafter' => 500 , 'tdclass' => 'key', 'email' => 'data\[register\]\[email\]','password' => 'data\[register\]\[password2\]');
to:
$components = array('view' => array('checkout','user'),'viewvar' => 'ctrl', 'lengthafter' => 500 , 'tdclass' => 'key', 'email' => 'data\[address\]\[CUSTOM_FIELD_COLUMN_NAME\]','password' => 'data\[address\]\[CUSTOM_FIELD_COLUMN_NAME\]');
where CUSTOM_FIELD_COLUMN_NAME should be replaced by the column name of your custom address field, in the file plugins/system/recaptcha.php