I have a web form which the users fill and the info send to server and stored on a database. I am worried that Robots might just fill in the form and I will end up with a database full of useless records. How can I prevent Robots from filling in my forms? I am thinking maybe something like Stackoverflow's robot detection, where if it thinks you are a robot, it asks you to verify that you are not. Is there a server-side API in Perl, Java or PHP?
There are several solutions.
Use a CAPTCHA. SO uses reCAPTCHA as far as I know.
Add an extra field to your form and hide it with CSS (display:none). A normal user would not see this field and therefore will not fill it. You check at the submission if this field is empty. If not, then you are dealing with a robot that has carefully filled out all form fields. This technique is usually referred to as a "honeypot".
Add a JavaScript timer function. At the page load it starts a value at zero and then increases it as time passes. A normal user would read and fill out your form for some time and only then submit it. A robot would just fill out and submit the form immediately upon receiving it. You check if the value has gone much from zero at the submission. If it has, then it is likely a real user. If you see just a couple of seconds (or even no value at all due to the robots not executing JavaScript) then it is likely a robot. This will however only work if you decide you will require your users have JavaScript on in order to perform "write" operations.
There are other techniques for sure. But these are quite simple and effective.