As it turned out, some spambots have already learned how to break through the protection in Javascript, but they have been breaking the captcha for quite some time.

In this regard, the question of creating a more complex for robots, but relatively simple protection for people, is ripe.

I think to do the following:
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1. Apply protection with javascript + cookies, like the one that is made in WP-Spamfree.

2. Hide the form from the page, display it via javascript.

3. Dynamically generate field IDs, for each page load its own

With the filing of "particularly smart" citizens, you can now call the captcha or the test for the addition of numbers "fascism" and shoot. Wellcome, spammers, so to speak. Well, your right :-) Although, if the comment is valuable, and the discussion is valuable for the commentator, then enter the captcha is easy.

For the rest, I think a little bit to improve the mechanism of the captcha. Say, break it into several pieces, part of the output image, and part - the background. Moreover, the symbol is formed by overlaying the background and the image.

For example, the upper part of the symbol in the background image, and the lower - in img. And this case is randomly generated. And for background use CSS Sprites technique ;-)

Well, the whole thing is also somehow shuffled with javascript.

Need ideas and facts.