A more thorough explanation:

The silent-witness theory is a method of authenticating and admitting evidence, such as a photograph, without the need for a witness to verify its authenticity. This can be done upon a sufficient showing of the reliability of the process of producing the evidence, including proof that the evidence has not been altered.

Let's say there is a photograph of a car accident. The silent-witness theory can be used to admit the photograph as evidence in court without the need for a witness to testify that the photograph is authentic. This can be done if it can be shown that the photograph was taken by a reliable source, such as a police officer, and that the photograph has not been altered in any way.

Another example could be a video recording of a crime. If it can be shown that the video was taken by a reliable source and has not been altered, it can be admitted as evidence without the need for a witness to testify to its authenticity.

These examples illustrate how the silent-witness theory can be used to authenticate and admit evidence without the need for a witness to testify to its authenticity, as long as the reliability of the process of producing the evidence can be shown.