To prevent spam comments from being added to your projects and images, Prevue uses a variety of different techniques to detect illegitimate feedback. The most noticeable method used to help in this fight is reCAPTCHA.
On all publicly-viewed projects where commenting is enabled, an "I'm not a robot" button will appear when adding a new item of feedback (shown above). Visitors are required to check this box to continue and add their comment. Once your visitors have successfully added at least one comment, they won't be asked to do this again — it's a one-time thing to safeguard your projects.
More often than not, completing this test is simply a matter of checking a box. However, some visitors may be required to pass further validation if they're considered to be higher risk — this will take the form of a very simple image test like the one shown below. Easy on humans, tough on bots.
You and your visitors will recognise reCaptcha — it's an initiative by Google and a widely-used technique to protect websites from spammers and bots. For more information, read the Google FAQ.