Unless your site is very heavily trafficked, bot coders aren't going to modify their scripts just to deal with you.

By the same obscurity-based argument, it's probably easier to just roll your own Captcha than installing/integrating/depending on a third-party library.

Please prove you're a human by typing "cat" below

that's true, but this form of captcha is more user friendly, as the user isn't even aware it's there.

Exactly. This isn't an end all be all, but it does up the security on your site.

It's like when you lock your bike, a focused attacker can open any lock with the right tools, but that shouldn't stop you from locking and using secondary deterrents like anti-theft skewers, or my favorite, simply locking it next to a nicer bike with a worse lock.

That's what I thought, until somebody reverse engineered the registration mechanism on my personal site which runs software I've written. I ended up having to turn registration off as I didn't have time to fix it properly.

Are you sure that somebody reverse-engineered it, or is it possible that someone's just got a set of rules generic enough to work on your site? From personal experience (with getting spammed), I suspect it's the latter.

It's always possible. I no longer remember exactly how it worked and why that made me think it had to be reverse engineered. This was many years ago now.

This is also an argument against using a standardized module like this, at least once it gains wider adoption.