Geo-Captcha & Geo-Blacklist is free wordpress plugin to shows a captcha image only to countries you don’t trust and allows you to disable comments for some countries.
To install
Login to wordpress (wp-admin).
In your admin dashboard click plugins and select Add New.
Type Geo-Captcha & Geo-Blacklist in the search field and click Search Plugins button.
Install Geo-Captcha & Geo-Blacklist.
After the successfully Installation click the activate Plugin link to activate the plugin.
[OR]
Download Geo-Captcha & Geo-Blacklist wordpress plugin. Download link.
Unzip and upload it to your WordPress wp-content/plugins directory.
Login to wp-admin. In your admin dashboard click plugins and activate the Geo-Captcha & Geo-Blacklist wordpress plugin