cutaia wrote: Well, then allow me to enlighten you. It's a grid of random pictures that changes on each page load. The person must click (for example) all the pictures that contain tigers before submitting the page. It seems like a damned good idea as it pretty much reqires a human to descern between pictures.
The problem of those is that it requires custom images for each board, and possibly many of them. Without customization, any bot can read assign tags to every image and thus solve it. Yes there is a "Anti-image-harvesting measures", but no big deal: Any spammer can download the kit and so he'll get access to the set of images. Even if they are encrypted, with some time it's not that hard to get them all... unless there is a huge number of images.
None the less, it can be a good method if the security is really good and if people use custom images.
Supposing a PHP generate the image from an invisible server folder. That image would have a random name for each cell of the grid. Then a similar method:
Pro (of the method):
- Easy to customize
- Very hard for bots (supposing custom images)
Con (of the method):
- Takes more disk space and space in the registration box
- Requires english knowledge/translation of the tags
- Not so good out-of-the-box