Abstract: Techniques for signing multimedia content and verifying received multimedia content that are both robust and accurate are provided. Invariant features are extracted from multimedia content, and certain attributes are computed. Multimedia content is quantized, and extracted invariant features and quantized original multimedia content are encrypted to form a digital signature. The multimedia content and digital signature may be verified even after the introduction of distortions by using content registration. In a preferred embodiment, a refined authentication technique is used to obtain a continuous distance measure, to verify the authenticity of multimedia content based on a pre-defined threshold.