Read Captcha from CaptchaImageHandler

The CaptchaImageHandler.aspx class of Microsoft ASP.net provides a captcha service. It accepts a parameter via an URL like

../CaptchaImageHandler.aspx?captcha=FLYq9H7jrlxOk7BzEvb9GQ==

and returns via HTTP an image including the captcha.

Is there a way to translate the parameter to the captcha?