Evidence can be authenticated in many different ways. That is why Rule 901 is unique from the other rules of evidence. 901 does not give a concrete method for laying the foundation and authenticating evidence, rather, it lays out a non-exhaustive list of different methods for proving that the piece of evidence "is what it claims to be."
In State v. Patterson, the court of appeals had to decide whether a trial judge abused his discretion by allowing in DNA evidence when there was a question of its authentication.
Brief facts of the case: Defendant left his hat at the crime scene after a robbery. Law enforcement tested the hat for DNA. They took the DNA they found from the hat and entered it into CODIS (The DNA database). A match came back to the defendant. After the defendant was arrested for the robbery, law enforcement took a buccal swab from him and matched his DNA from the swab with DNA from the hat.
The defense argued that the state did not have the proper witness to testify about the DNA entered into the database. They also objected to the authentication of the DNA that was already in the database from the defendant from a previous conviction.
The court allowed in the DNA evidence because the state's witnesses testified that they had first-hand knowledge of the procedure for using the database and they personally verified the results. The court also found that the DNA results had specific characteristics that set them apart.
As to the chain of custody for the original DNA in the database, the court held:
Additionally, although a perfect chain of custody was not shown for the DNA evidence that was already contained in the CODIS database, we believe the authenticity of the DNA results were nevertheless established through the independent testing of Patterson's DNA profile. Boehm was qualified as an expert in DNA analysis and she testified she matched the DNA profile taken off Patterson after his arrest with the DNA profile taken off the fedora found at the crime scene. State v. Patterson, No. 2016-000863, 2019 WL 99151, at *4 (S.C. Ct. App. Jan. 4, 2019)
What I take away from this case are two things. First, a trial judge is given broad discretion when it comes to authentication of evidence. A trial judge has to make the determination that piece of evidence is what it claims to be. They are in the best position to make that judgment call. Second, authentication really is a judgment call. As opposed to other rules, such as hearsay, character evidence, impeachment, etc., the rule for authentication is much more nuanced. And this makes sense. There are thousands and thousands of different types of evidence, and each one requires different methods for determining if that piece of evidence is actually authentic.
This doesn't mean that a party can just throw any witness on the stand to claim that they believe the evidence is real, but it does mean that absolute perfection is not required.
Also keep in mind, just because a piece of evidence is authenticated and admitted, the opposing party can still attack the credibility of the evidence to the jury. Weight vs. admissibility.