Content with flashes, bright colors, and repeated patterns can cause seizures and migraines when viewed by people with photosensitivity. Exposure to seizure-inducing content is a serious risk in online environments, as evidenced by documented instances of people with photosensitivity being exposed to seizure-inducing material while playing video games or using social media.My thesis focuses on improving online safety and accessibility for people with photosensitivity by measuring the prevalence of seizure-inducing content online, developing new tools for detecting seizure-inducing content, and constructing a broad framework for protecting against seizure-inducing content at the level of content creators, platforms, and content consumers. Through this work, I hope to help build a better understanding of the current state of photosensitive risk online and contribute new solutions for mitigating seizure-inducing content with minimal adverse effects on the browsing experience for users with photosensitivity.