title: Why CasperJS and browsers show different behaviors with CAPTCHA?
body: <p>I'm using CasperJS to automate some of my tasks. CasperJS will meet captcha when exploring web pages. However, when I use browsers (chrome and safari) to access the page, I don't need to input the captcha. I try to set the <code>userAgent</code> option with the same value in browsers, but it does not work.</p>
  
  <p>I want to know why CasperJS and browsers show different behaviors. And how can CasperJS pretend to be real browser? In other words, the web server cannot distinguish them. 
  Thanks.</p>