reCAPTCHA using IE 8 (black spot behind letters)

Hello, I work for a company that uses IE 8 as default browser (it's not my call!). They have been suffering some issues regarding the captchas: they appear with a black spot behind the frase. This seems to increase the already difficult captcha and they want to remove it (some users tested the same page using Chrome and it doesn't appear there). I truly appreciate your help and sorry for my poor third world English :) Regards! -- 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/1gYXIc9.