It show different captcha in different computer. Why?

I've been using reCaptcha for quite some time but yesterday I got a call from a friend saying that page show different type captcha sometimes. This is how I see my recaptcha. and this is how my friend sees my recaptcha. Why? -- You received this message because you are subscribed to the Google Groups "reCAPTCHA" group. To unsubscribe from this group and stop receiving emails from it, send an email to recaptcha+unsubscribe@googlegroups.com. To post to this group, send email to recaptcha@googlegroups.com. Visit this group at http://bit.ly/1dkFnYd. For more options, visit http://bit.ly/P65DvS.