A processing device is provided for processing an image obtained by imaging the inside of the oral cavity for use in diagnosis of the inside of the oral cavity. The processing device includes at least one processor. The at least one processor performs processing for acquiring one or more determination images of a subject through a camera for capturing an image of the subject including at least a part of a user's oral cavity, determining a possibility of contracting a predetermined disease based on a trained determination model stored in a memory to determine the possibility of contracting the predetermined disease and the one or more acquired determination images, and outputting information indicating the determined possibility of contracting the predetermined disease.