Soft authentication techniques for images

Due to the nature of modern communications, intentional or unintentional modifications might be introduced into the images, transmitted in time or spatial domain, by a human, source encoders/decoders or the channel. Content based authentication schemes aim to verify the authenticity of the content of an image instead of the image data. Content modification is defined as the addition or deletion of objects from the image, changing the position of objects or changing other image features such as the edges, colors or texture. The object may be two or three dimensional. This paper discusses the soft image authentication techniques developed over the features in spatial and frequency domains. Soft authentication, in contrast to the standard hard authentication, tolerates modifications in image data as long as the content is intact. At the same time, soft authentication algorithms should be very sensitive to forgeries.