how do you protect a site against spam without using captcha [closed]

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CAPTCHA presents a user experience problem.

Are there alternatives to CAPTCHA that deal with most attacks?

We have already tried and am currently using JCaptcha. We are considering reCaptcha - however it is problematic because it requires a connection to the internet to perform catpcha verification.

Answer 1

To better help you, can you elaborate on what it is that's being spammed? E.g. registration form, login form, mailing list registration etc. Would it be feasible for the user to click on a link in a confirmation e-mail before the action is preformed?

Don't use any type of captcha. In third world countries there are services were it costs $1 to solve 70 captchas.

Use a honeypot, where an input field is hidden so no user (i.e. actual person) would fill it in but a spambot would. If the form is submitted with a non-empty field then you know it's spam.

There are other measures that can be taken too. ASIRRA, by Microsoft, is an alternative where you select pictures of cats or dogs and if you selected all correctly you are not a bot.

Answer 2

I've seen things like, "Drag only the apples to the basket". Might be a bit more overhead though.

Answer 3

If you are a small enough target, probably any test that is not already out there will work. It is generally not worth someone writing an automated way of beating your test, just for your website.

One method I've heard of is to use google images to download, say, 100 pictures of trees, 100 of shoes, 100 of ducks, and so forth; then pick 5 random pictures, each from a different category, and ask "please select identify the subject of each picture", with a dropdown list with "trees, shoes, ducks....". Make sure you don't give away the answer in the html, of course. Black & white Line drawings work better for this than photos, since the colour might give the answer away for trees. Make sure you limit the rate someone can answer. Randomly matching 5 pictures has a 1/3125 chance of succeeding. If you download the pictures in advance, you won't need network access.