Limits of Fourth Amendment Protections in Private Automated Hash-Based Monitoring: United States v. Rosenschein

Introduction

United States v. Rosenschein (10th Cir. 2025) addresses whether private‐sector content‐scanning tools and internet chatroom operators can trigger Fourth Amendment protection when they detect and report illicit material. In 2016, an anonymous user uploaded child pornography images to Chatstep, a public chat service that uses Microsoft’s PhotoDNA to hash and compare images against a database of known illegal content. Chatstep reported the matching files and IP data to the National Center for Missing & Exploited Children (NCMEC), which referred the matter to local law enforcement in Bernalillo County, New Mexico. A search warrant followed, revealing thousands of child-pornography images on Guy Rosenschein’s devices. Rosenschein moved to suppress evidence under the Fourth Amendment (arguing private scanning was a “government search”), to challenge the warrant affidavits under Franks v. Delaware, and to compel disclosure of NCMEC/Microsoft reporting algorithms and expert reports. The district court denied each motion; Rosenschein pleaded guilty but reserved his right to appeal those denials.

Summary of the Judgment

The Tenth Circuit unanimously affirmed all denials. Key holdings:

No Fourth Amendment search: Chatstep and Microsoft were not government agents. Even if they were, users have no reasonable privacy expectation over images posted to a public chatroom.
No Franks violation: The warrant affidavits contained no materially false statements or omissions that would undermine probable cause.
Discovery & experts: The district court acted within its discretion in refusing to compel production of NCMEC’s internal algorithms (testimonial evidence sufficed) and in declining to order expert reports prior to a suppression hearing.

Analysis

Precedents Cited

United States v. Jacobsen (466 U.S. 109): Private individuals not acting as government agents do not implicate the Fourth Amendment.
United States v. Souza (10th Cir. 2001): Two-pronged test for “government agent” status—government knowledge/acquiescence and private intent to assist law enforcement.
United States v. Ackerman (10th Cir. 2016): NCMEC’s funded, statutory mission to aid law enforcement made it a government actor when it opened forwarded emails.
Carpenter v. United States (585 U.S. 296): Establishes that a warrant is required when an individual has a reasonable societal privacy expectation in data.
Jones (565 U.S. 400): Fourth Amendment also protects against physical trespass for information gathering.
Miller (425 U.S. 435) & subsequent circuits (Morel, Lifshitz, Guest): No privacy expectation in information “voluntarily exposed” to third parties or public online forums.
Franks v. Delaware (438 U.S. 154): Suppression requires a substantial, intentional or reckless affidavit misstatement or omission.
Youngblood (488 U.S. 51): To dismiss for lost evidence, must show government bad faith.
Simpson (10th Cir. 1998): Generalized descriptions of child pornography in warrant affidavits suffice for probable cause.

Legal Reasoning

The court’s reasoning unfolded in three main steps:

Government-agent inquiry: Under Jacobsen/Souza, private actors only become government agents if (1) government knows of and acquiesces in the conduct, and (2) the private party intends to assist law enforcement. Here, Chatstep and Microsoft acted to protect reputations, serve users, and meet their own business objectives. NCMEC’s statutory duty to receive tips did not transform them into state actors.
Expectation of privacy: Even assuming government involvement, Rosenschein “knowingly exposed” his uploads to a public, free chat service. No reasonable user would expect privacy in content shared with strangers or scanners. This aligns with Miller and its progeny rejecting privacy claims over third-party or public Internet transmissions.
Franks & other motions: The affidavit’s statements about “hash values” and image descriptions were accurate, non-misleading, or immaterial. The warrant judge received sufficient facts to find probable cause. No evidence of Franks-level recklessness or bad faith appeared. Discovery of algorithmic details and pre-hearing expert reports were discretionary, and the court properly declined.

Impact

United States v. Rosenschein clarifies several points in digital Fourth Amendment law:

Private automated monitoring: Platforms using hash-based scanning (e.g., PhotoDNA) remain private actors when they detect illegal content under their business policies. Their actions do not trigger Fourth Amendment scrutiny absent significant government orchestration.
Limited privacy expectations online: Users bear the risk that content voluntarily posted to public or semi-public forums can be scanned, logged, reported, and used in criminal proceedings.
Preservation & discovery: Absent bad faith, private parties’ loss of relevant data does not demand dismissal. Testimonial evidence can satisfy a defendant’s need for technical explanations of third-party systems.
Procedural safeguards: Franks challenges remain a high bar—defendants must point to intentional or reckless affidavit errors that matter to probable cause.

Complex Concepts Simplified

Hash Value: A unique alphanumeric “fingerprint” generated by an algorithm from a larger file (e.g., an image). If two files produce the same hash, they’re virtually guaranteed to be identical—even if slightly altered.
PhotoDNA: Microsoft-developed software that converts images into hash values and compares them against a database of known illegal images. Fast, automated, and highly accurate.
Reasonable Expectation of Privacy: A two-part test (subjective + societal) determining if a person is entitled to Fourth Amendment protection. If you “knowingly expose” something to the public or third parties, you lose that protection.
Franks Hearing: A pre-trial proceeding where a defendant may attack a warrant affidavit for false statements or omissions. Only significant, intentional, or reckless errors that affect probable cause can warrant suppression.
Government Agent Test: Courts ask whether private conduct was effectively under government control or intended to assist law enforcement. Absent both, there is no “state action.”

Conclusion

United States v. Rosenschein establishes that private, automated scanning of user-uploaded content—driven by corporate policy and public-safety goals—does not constitute a Fourth Amendment search. It reaffirms that users forfeit privacy claims when they share content on public Internet platforms and clarifies the strict standards governing affidavit challenges and third-party discovery. This decision provides important guidance for online service providers, digital forensics experts, and criminal practitioners navigating the intersection of technology and constitutional protections.