Although I have not implemented captcha in any login form, but , i do have some fair idea of it. So i am sharing my thoughts on it
a. captcha is any randon alphanumeric
string used for authentication in login form. We can write a simple
java class to generate random
aplhanumeric strings which can be shown on
jsp page. I assume you know how to display a captcha string on jsp page and use it in validation in furthur processing after form submission.
b. you can use website like
http://recaptcha.net/ to have autogenerated captcha
Below mentioned is the link of a pdf from "Spring in Practice" book by Manning publication.
Refer to
section 4.4 Use CAPTCHAs to prevent automated user account creation where it is mentioned how to use captcha in spring login form.
http://www.manning.com/wheeler/SIP_Wheeler_MEAP_ch4.pdf
Hope all this explanation helps you
~ abhay
Oracle certified JPA Developer (1Z0-898),Oracle certified Java 8 Programmer I (1Z0-808), Oracle Java Web Service Developer (1z0-897), Oracle certified Java 7 Programmer, SCJA 1.0, SCJP 5.0, SCWCD 5.0, Oracle SQL Fundamentals I, CIW Certified Ecommerce specialist