Biometric templates may be stored in the memory of readers, limiting the number of users by the reader memory size (there are reader models that have been manufactured with a storage capacity of up to 50,000 templates). User templates may also be stored in the memory of the smart card, thereby removing all limits to the number of system users (finger-only identification is not possible with this technology), or a central server PC can act as the template host. For systems where a central server is employed, known as "server-based verification", readers first read the biometric data of the user and then forward it to the main computer for processing. Server-based systems support a large number of users but are dependent on the reliability of the central server, as well as communication lines.
Mina Crandon claimed to materialize a "spirit hand", but when examined by biologists the hand was discovered to be made from a piece of carved animal liver. The German apport medium Heinrich Melzer was discovered to be a fraud in 1926. In a séance psychical researchers found that Melzer had small stones attached to the back of his ears by flesh coloured tape. Psychical researchers who investigated the mediumship of Maria Silbert revealed that she used her feet and toes to move objects in the séance room.
In the 1920s the British medium Charles Albert Beare duped the Spiritualist organization the Temple of Light into believing he had genuine mediumship powers. In 1931 Beare published a confession in the newspaper Daily Express. In the confession he stated "I have deceived hundreds of people…. I have been guilty of fraud and deception in spiritualistic practices by pretending that I was controlled by a spirit guide…. I am frankly and whole-heartedly sorry that I have allowed myself to deceive people." Due to the exposure of William Hope and other fraudulent spiritualists, Arthur Conan Doyle in the 1920s led a mass resignation of eighty-four members of the Society for Psychical Research, as they believed the Society was opposed to spiritualism.
Many 19th century mediums were discovered to be engaged in fraud. While advocates of mediumship claim that their experiences are genuine, the Encyclopædia Britannica article on spiritualism notes in reference to a case in the 19th century that "...one by one, the Spiritualist mediums were discovered to be engaged in fraud, sometimes employing the techniques of stage magicians in their attempts to convince people of their clairvoyant powers." The article also notes that "the exposure of widespread fraud within the spiritualist movement severely damaged its reputation and pushed it to the fringes of society in the United States."