how to get captcha when using the "post request"

[work4seo]

i want to spam on this url:http://standard.gm/site/culture/3452-The-Soninke-Nyancho-Kaabu.html
i got the post data like this:

action=comment&cmd=add&COMMENT_article_id=3121&COMMENT_author=username&COMMENT_email=adfjdkjf%40gmail.com&COMMENT_www=URL&COMMENT_description=nice%20post&COMMENT_captcha=68ff6df4&template_output=box%2Fcomments_add

how can i get the captcha when using post?