To install the helper, you need to uncompress it at first. After uncompressing it, you will see the following files in the target folder: BypassCaptchaForZennoPoster.dll and bypasscaptcha_key.txt .
Then you need to copy these two files into ZennoPoster's own folder.
Go to ZennoPoster's folder and open the file bypasscaptcha_key.txt . Open it and erase all old text, fill your bypasscaptcha key there. Do not have one? Order it now.