Which of the following is considered an X-ray accessory?

The correct choice is cassettes, as they serve an integral role in radiographic imaging. Cassettes are used to hold the radiographic film or digital detectors in place during exposure to X-rays. They are essential for capturing the images produced by the X-ray machine and are specifically designed to maintain the integrity of the film or detector while providing a light-tight atmosphere.

On the other hand, collimators and filters are considered accessories or components that modify or enhance the X-ray beam. Collimators limit the size and shape of the X-ray beam to reduce patient exposure and improve image quality. Filtration is used to absorb low-energy X-rays, which do not contribute to the image but increase radiation exposure to the patient. An X-ray tube is the primary component that generates the X-rays but is not classified as an accessory. Cassettes, therefore, are distinctly recognized as accessories in the context of X-ray imaging systems.