So a human being won't see that field (unless they have CSS turned off, in which case they'll see the label and leave it blank) but a spam robot will fill it in. Any post with that field populated must be from a spam robot.
Here's a simple math captcha by Phil Haack. It even works with javascript disabled.
In his own words:
The way it works is that it renders some javascript to perform a really simple calculation and write the answer into a hidden text field using javascript. When the user submits the form, we take the submitted value from the hidden form field, combine it with a secret salt value, and then hash the whole thing together. We then compare this value with the hash of the expected answer, which is stored in a hidden form field base64 encoded. If javascript is disabled, then we render out the question as text alongside a visible text field, thus giving users reading your site via non-javascript browsers a chance to comment.
MTCaptcha is a reCaptcha alternative captcha service that supports invisible captchas similar to the recently launched reCaptcha V3, where its invisible to most users but shows a captcha if it feels the traffic is risky.
If you mean - use captcha that a human can't see as a human validation test - i think it's impossible.
This way a robot ignoring the captcha will pass for a real person! Seems like a trap for a naive spam robot.
If you want your captcha-protected site to work with clients that have no javascript - then you should hardcode it into html.
Also, if you can reliably identify trusted users (either by judgment call or by detecting some usage pattern) - you can let them post to your site without captcha.
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添加一个新的输入字段，将其标记为“请留空”，使用 CSS 隐藏它，如果该字段已填写，则忽略该帖子。像这样：
所以人们不会看到该字段（除非他们将 CSS 变成关闭，在这种情况下，他们会看到标签并将其留空），但垃圾邮件机器人会填写它。填充该字段的任何帖子都必须来自垃圾邮件机器人。
Add a new input field, label it "Please leave blank", hide it using CSS, and ignore the post if that field is filled in. Something like this:
So a human being won't see that field (unless they have CSS turned off, in which case they'll see the label and leave it blank) but a spam robot will fill it in. Any post with that field populated must be from a spam robot.
这里由 Phil Haack 编写的一个简单的数学验证码。 它甚至可以在禁用 JavaScript 的情况下工作。
用他自己的话说：
Here's a simple math captcha by Phil Haack. It even works with javascript disabled.
In his own words:
我使用了 Display:None 文本框的技术，并拒绝任何填写该文本框的提交，并且运气很好。
I've used the technique of a Display:None text box, and rejecting any submission that fills it in and had pretty good luck with that.
谷歌正在推出“隐形 ReCAPTCHA”（https://www .google.com/recaptcha/intro/comingsoon/invisible.html），我的网站已列入白名单。 目前正在实施它，但是文档还没有那么详细......:)
For what it's worth Google is rolling out 'Invisible ReCAPTCHA' (https://www.google.com/recaptcha/intro/comingsoon/invisible.html), I already got whitelisted with my site. At the moment implementing it, however the docs aren't that elaborated...:)
MTCaptcha 是一种 reCaptcha 替代验证码服务，支持隐形验证码，类似于最近推出的 reCaptcha V3，其中大多数人看不到它用户，但如果认为流量有风险，则会显示验证码。
MTCaptcha is a reCaptcha alternative captcha service that supports invisible captchas similar to the recently launched reCaptcha V3, where its invisible to most users but shows a captcha if it feels the traffic is risky.
如果你的意思是 - 使用人类看不到的验证码作为人类验证测试 - 我认为这是不可能的。
这样忽略验证码的机器人就会冒充真人！ 看起来像是一个天真的垃圾邮件机器人的陷阱。
如果您希望受验证码保护的网站能够与没有 javascript 的客户端一起使用 - 那么您应该将其硬编码为 html。
此外，如果您可以可靠地识别受信任的用户（通过判断调用或通过检测某些使用模式） - 您可以让他们在没有验证码的情况下发布到您的网站。
If you mean - use captcha that a human can't see as a human validation test - i think it's impossible.
This way a robot ignoring the captcha will pass for a real person! Seems like a trap for a naive spam robot.
If you want your captcha-protected site to work with clients that have no javascript - then you should hardcode it into html.
Also, if you can reliably identify trusted users (either by judgment call or by detecting some usage pattern) - you can let them post to your site without captcha.