1. A method for image tamper detection, comprising the steps of: (a) computing a thumbnail of an original image; (b) embedding the computed thumbnail in the original image to create a marked image; (c) transmitting the marked image to a recipient; (d) extracting the embedded thumbnail from the transmitted marked image; (e) computing a new thumbnail of the received image; (f) differencing the extracted thumbnail from the new thumbnail to create a difference image that represents the similarity of the two thumbnails; (g) alerting if the difference image shows the two thumbnails are not sufficiently similar; and (h) authenticating the image if the difference image shows the two thumbnails are sufficiently similar.