This book constitutes the refereed proceedings of the 12th International Workshop, OMIA 2025, Held in Conjunction with MICCAI 2025, Daejeon, South Korea, September 27, 2025. The 17 full papers presented in this book were carefully selected and reviewed from 33 submissions.This workshop aimed to bring together scientists, clinicians, and students from multiple disciplines in the growing ophthalmic image analysis community such as electronic engineering, computer science, mathematics, and medicine to discuss the latest advancements in the field.