Try below approach,
$('#bfCaptchaEntry').on('click', myfunction);
or in case jQuery is not an absolute necessaity then try below,
document.getElementById('bfCaptchaEntry').onclick = myfunction;
However the above method has few drawbacks as it set onclick as a property rather than being registered as handler...
Read more on this post https://stackoverflow.com/a/6348597/297641