In this talk at the FOSDEM conference, the speaker discusses similarity detection and its use in maintaining the integrity of a website. They explain the problem of ensuring a safe online platform and the need for both automation and human review in content moderation. The speaker introduces different technologies for image and video hashing, such as PDQ and Video PDQ, and explains how they can be used for similarity detection. They also mention the SimSearchNet++ algorithm and the open-source SSCD tool. The speaker concludes by introducing HMA, a turnkey open-source solution that can be installed on a platform to enforce integrity policies. They also mention the threat exchange platform for sharing hashes with other organizations.