Limit rate of login attempts and block ip temporarily (Up to 10 minutes). It is protecting from brute force attack. Fraud ip detection. Features:- - Captcha Verification - Limit the number of login attempts and block ip temporarily. - Quick proxy ip detection - Light weight plugin - Mechanism for slow down brute force attack - Detect fraud ips. - Redirect to home page, when abnormal request (It will stop hacking tools) https://wordpress.org/plugins/wp-limit-login-attempts/
Had a look at the screenshots on the link you displayed and the captcha is easy to break. You need to add distortion to the image, add different font types for different letters, add different colours for different letters and make them appear in different locations every time a captcha is loaded.