Science advances by extending our senses beyond the limits of human perception, pushing the boundaries of what we can observe. In photon science, imaging detectors serve as the eyes of science, translating invisible processes into measurable and analysable data. Behind every image lies a deep understanding of how detectors see, respond and perform. At facilities like the European XFEL, the world's most powerful X-ray free-electron laser located in the Hamburg metropolitan area, imaging detectors capture ultrashort X-ray flashes at MHz frame rates and with high dynamic range. Without these advanced detectors, even the brightest X-ray laser beam would remain invisible. They help to reveal what would otherwise stay hidden, such as the structure of biomolecules, the behaviour of novel materials, and matter under extreme conditions. But how do we know they will perform as expected? And how do we design systems capable of “seeing” the invisible?