Maighstir: Especially when it comes to security, it's far too easy to fuck up when trying to invent a better wheel.
Lukaszmik: As an old-school programmer, I find this approach worrisome.
We are not talking about some multi-million-line code here. If you are using third-party scripts on your web site, and your web site stops functioning when they are blocked, that's both poor implementation and poor security practice.
If it's something critical to your web site, then it should behoove you to study those libraries until you can write your own version, understanding exactly what they do, and plugging any potential security holes.
I realize this is not something looked favorably on in current "cheapest way possible" business, but I would have been professionally ashamed to make my code utterly dependent on the availability of third-party libraries for something as simple as a web site.
At worst, host those elements on your own server!
Now, I'm not saying I agree with the link-to-script-on-thirdparty-host bandwagon, and absolutely would prefer that everything necessary be hosted by the first-party, but creating a half-decent CAPTCHA isn't all too easy.
Scrambled-text CAPTCHAs are easy to create, but are also by now easier to pass for a computer than a human, thus completely invalidating the point of them. Which is why we're now often told to identify objects in an image - the thing about that, though, is that you need a fairly large library of images
and relevant metadata for the system to be effective, something I doubt GOG have, or have the resources to create.
Granted, Google's system is not only for validating that you're a human, but also used as training data for their image recognition algorithms (some images you get are "we know what this is, do you?" while others are "we're not sure what this is, can you tell us?", and you don't get to know which is which), so in time said system will be useless too, at which point new methods will have to have been invented.