CAPTCHA/fr

Les CAPTCHAs (raccourci de "Completely Automated Public Turing test to tell Computers and Humans Apart") sont utilisés sur les wikis Wikimedia, via l'extension, comme moyen d'empêcher le spam autant que possible, et de démasquer les spammeurs. Sur la plupart des wikis, un utilisateur peut rencontrer un CAPTCHA quand il essaie de créer un compte, une nouvelle page, ou quand il ajoute un lien externe sur une page.

On pt.wiki, in 2008–2013 the CAPTCHA was also "temporarily" shown on every edit of unregistered and new users, allegedly to reduce vandalism (see discussion and 41745).

L'implémentation actuelle du CAPTCHA pose un certain nombre de problèmes.


 * They are only available in English (5309): the words used by our CAPTCHAs, however they are created, should be in the user's language. An unknown number of new users and edits are lost from non-English speaking people.
 * They violate accessibility principles (4845).
 * They don't effectively prevent bots from spamming.



Alternatives pour une implémentation future éventuelle


CAPTCHAs image
Les images Captcha n'ont pas besoin de texte à saisir ce qui est pratique avec les mobiles et les problèmes de traduction. Certaines idées basées sur les images :


 * Find the different one (view prototype). Several images from the same category (e.g., people) are shown mixed with one image from a different category (e.g., cat). Humans should be able to recognise which is the different one. Note that in this case, the question is always the same (find the different one) and the categories used are not exposed to the user.
 * Find all images of a kind (view prototype). Images from two or more categories are presented together. The user is explicitly asked to find all the images of a given type (e.g., all images of people wearing glasses).
 * Tag images (view prototype). The user is presented with images that contain some tagged elements and options to pick the correct tag (e.g., is it a bird? is it a plane?).

La partie difficile ici est comment créer des images et vérifier les données d'une manière qui ne soit pas exploitable par les robots spammeurs. Vous devez posséder un grand nombre de CAPTCHAs (au mieux des centaines de milliers), sinon il suffit à l'attaquant de calquer la base de données de vos CAPTCHA. Si vous utilisez un dépôt public d'images (tel que Commons), ou une source de données ouvertes (telle que les catégories Commons), il y a des chances que l'attaquant puisse identifier le CAPTCHA et sa source et ainsi trouver la solution.



Remplacer le CAPTCHA par un pot de miel
Une possibilité pour éviter les problèmes dûs aux langues avec le CAPTCHA est simplement de le supprimer et de le remplacer par un pot de miel.



Un clone de reCAPTCHA élevé à la maison
Write a version of reCAPTCHA that uses document images that have been processed by MediaWiki's ProofreadPage extension for Wikisource: WikiCAPTCHA. In other words, a CAPTCHA that feeds data to ProofreadPage to augment its OCR processing. You might build on [//github.com/CristianCantoro/wikicaptcha existing code]. It is worth noting that "reCAPTCHA hold no specific patents for the technology behind their text CAPTCHA algorithms (At least none they discuss on their website or are able to be found on the US Patents & Trademark Office site", according to one blogger ).

Also discussed at Wikimania 2012 with the presentation Wikicaptcha: a ReCAPTCHA-like solution for Wikisource

The advantage of this approach is that we can make the latent work force currently wasted in CAPTCHA into profit for a Wikimedia project (Wikisource); and that we can start with a limited data set. In fact, working the reCaptcha way we could create some sort of bootstrap data set, then show people a mix of captchas with known and unknown solutions, and use the known ones for verification and the unknown ones for generating more data. But that is not easy and should get significant focus in the project if you want a CAPTCHA system which is of any practical use at the end.

Accessibility
The accessibility of our current CAPTCHA is extremely bad. If the user has impaired eyesight or uses a screenreader the text-based CAPTCHA is almost entirely inaccessible to them. A handful of our larger wikis solve this via a volunteer-run account request system. Alternatives like image CAPTCHAs still violate accessibility principles (4845), so an alternative such as an audio CAPTCHA should be considered.