Steps to reproduce the issue

Use recaptcha plugin in custom component. Use multiple instances of it so each instance has it's own input name.

When you call the recaptcha plugin to validate you can pass the $code to validate instead of the "standard" code from input.

see the function declaration: public function onCheckAnswer($code = null)

e.g.

$alldata = JFactory::getApplication()->input;
$cresponse = $alldata->get('grecaptcharesponse','','string'); //here we have the catcha code to validate

//call captcha plugin to validate code
JPluginHelper::importPlugin('captcha');
$dispatcher = JEventDispatcher::getInstance();

$res = $dispatcher->trigger('onCheckAnswer',$cresponse);

Expected result

A true validation of the $cresponce

Actual result

Always false

System information (as much as possible)

Joomla! 3.4.4 Stable [ Ember ] 8-September-2015 21:30 GMT
PHP: 5.4.43
Mysql: 5.5.42-37.1-log

Additional comments

The issue is on the onCheckReponse function of the captch plugin where has the $code param that your are able to pass but in true code the $code param is totally ignored.

I have a solution to propose that working ok:

in /plugins/captcha/recaptcha.php replace (about line 127):

$response = $input->get('g-recaptcha-response', '', 'string');

with:

if (!empty($code))
$response = $code;
else
$response = $input->get('g-recaptcha-response', '', 'string');

And issue will be solved.

thanks and i hope helped

christopher