Authentication and Admissibility of ALPR Evidence

This guide uses the Federal Rules of Evidence as the reference point. Most criminal cases are in state court under state rules, which are often similar but not identical. For the short version, see can Flock camera evidence be used in court?

Authentication: is it what it claims to be?

Rule 901(a) requires the side offering evidence to produce “evidence sufficient to support a finding that the item is what the proponent claims it is.” An ALPR record usually claims several things at once: this image was captured by this camera, at this time and place, and this is the plate text the software read from it. Common ways to authenticate it:

• A witness with knowledge, such as an agency’s ALPR administrator, who explains how the record was produced and retrieved.
• Evidence about the process or system: “evidence describing a process or system and showing that it produces an accurate result” (Rule 901(b)(9)).
• A certification: Rule 902(13) allows a record “generated by an electronic process or system that produces an accurate result” to be admitted on a qualified person’s certification, with advance notice to the other side.

The phrase “produces an accurate result” is where ALPR evidence can be tested. Published accuracy data is thin. Flock’s per-read accuracy claim has no published method, and agency figures mostly measure wrong alerts, not reads. See plate misreads and accuracy. Time stamps and camera locations depend on configuration, and the plate text is software output, not something a person checked.

The judge decides these preliminary questions. Under Rule 104(a), the court “is not bound by evidence rules” other than privilege when it does.

Hearsay and machine-generated records

The hearsay rule applies to “statements,” and Rule 801(a) defines a statement as “a person’s oral assertion, written assertion, or nonverbal conduct.” That raises a threshold question: is a plate read generated by software, with no person involved, hearsay at all? The answer can depend on how much human input went into the record and on the jurisdiction’s case law.

Records with human input are different. A hotlist entry typed in by an officer, a note on why a search was run, or a report summarizing ALPR results contains people’s assertions. These are often offered as records of a regularly conducted activity under Rule 803(6). That exception requires, among other things, that the record was made at or near the time by someone with knowledge as a regular practice. It doesn’t apply if the opponent shows the source or method of preparation “indicate[s] a lack of trustworthiness.”

The image vs. the plate text

Rule 1002 requires an original “writing, recording, or photograph” to prove its content, unless the rules provide otherwise. In ALPR cases, the photograph and the plate text are different things. The text is the software’s reading of the image. If the question is what plate the car carried, the image is the better evidence of that, and the defense will want the full-resolution original rather than a thumbnail or a summary in a report. See requesting ALPR records in discovery.

The Confrontation Clause

The Sixth Amendment gives a defendant the right to confront the witnesses against them. In Melendez-Diaz v. Massachusetts (2009), the Supreme Court held that sworn lab certificates reporting forensic results were testimonial, and that admitting them without the analysts testifying violated that right. Whether, and when, ALPR records or certifications about them are testimonial is a question we haven’t found the Supreme Court addressing. It may matter most when a certification or report, rather than the raw data, is offered in place of a live witness.

Misleading or prejudicial evidence

Even relevant evidence can be excluded if its probative value is “substantially outweighed by a danger of” unfair prejudice, confusing the issues, or “misleading the jury” (Rule 403). With ALPR evidence, the concern can be presentation: a map of reads or a summary that implies more certainty, or more about who was driving, than the records support.

Admissibility vs. weight

The bar for admission is relatively low. Once a record is admitted, the jury decides what it proves. Accuracy, completeness and who was driving are usually argued as questions of weight, often with the help of an expert witness. Separately, evidence obtained unlawfully may be challenged before trial in a motion to suppress.

Questions a defense attorney may investigate

• How does the prosecution plan to authenticate the records: a live witness, a certification, or testimony about the system?
• Was notice given for any certification, and does it actually show the system “produces an accurate result”?
• Which parts of the record involved human input, such as hotlist entries, notes and reports?
• Is the original image available at full resolution, and does it match the recorded plate text?
• Are maps, summaries or reports being offered in place of the underlying records?