To provide an image data alteration detection device, an image data alteration detection method, and a data structure of image data that can easily detect an alteration in image data. Metadata in image data includes a first hash value calculated based on predetermined data, a second hash value calculated based on a character string of a script, and the script. An image alteration detection device calculates a third hash value based on the predetermined data and the script included in the metadata, calculates a fourth hash value based on a character string of the script included in the metadata, compares the first hash value included in the metadata with the calculated third hash value and the second hash value included in the metadata with the calculated fourth hash value, and detects that the image data is altered when one of the values is not equal.