An imaging apparatus includes an image data generating unit, an authentication data generating unit, a receiving unit and an authentication unit. The image data generating unit generates first image data. The authentication data generating unit generates first authentication data from the first image data. The receiving unit receives second image data and second authentication data from an external device, wherein both the second image data and the second authentication data are generated by a second imaging apparatus, and the second authentication data is generated from the second image data. The authentication unit has (a) a first authentication mode where the authentication unit authenticates, using the first authentication data, whether the first image data has been altered, and (b) a second authentication mode where the authentication unit authenticates, using the second authentication data, whether the second image data has been altered.