Zurich's Digital Archives Are Full of the Same Image Twice — Here's What Officials and Experts Are Saying

Zurich's public institutions are sitting on a storage problem hiding in plain sight. Duplicate images — identical or near-identical digital files stored multiple times across disconnected systems — have quietly consumed significant server capacity at municipal archives, university repositories and cultural institutions across the city. The issue came into sharper focus this spring after Stadtarchiv Zürich, the city's official historical records office on Neumarkt, completed an internal audit of its digital holdings and found a substantial share of catalogued image files were redundant entries.

The audit did not produce a public figure, but archivists familiar with the process described the problem as structural rather than accidental. When institutions digitise physical collections in waves — as many Swiss cultural bodies did during pandemic-era projects between 2020 and 2022 — the same photograph or document often enters the system more than once, tagged under different metadata schemas and stored in separate folders by different teams.

Why the Problem Is Worse Than It Looks

The stakes go beyond hard drive costs. Duplicate entries create confusion in public-facing search tools, dilute cataloguing quality and complicate legal questions around rights management. For a city like Zurich, whose cultural memory institutions — including the Zentralbibliothek on Zähringerplatz and the Museum Rietberg in Rieterpark — have invested heavily in digital access over the past decade, the credibility of those tools depends on clean, reliable data.

ETH Zurich's Digital Humanities Lab, based on the Hönggerberg campus, has been working on automated deduplication methods for image collections since at least 2023. Researchers there have applied perceptual hashing and machine-learning comparison tools to large photographic datasets, finding that duplicate rates in institutional collections can range from under five percent in tightly managed archives to more than twenty percent in collections digitised under time pressure. Those figures are consistent with patterns documented in comparable European digitisation projects in Germany and the Netherlands.

Officials at the city's Amt für Städtebau, which maintains its own visual archive of planning documents and architectural surveys, have acknowledged the issue in internal working groups without making public statements. The broader conversation has drawn in cantonal-level records managers as well, particularly since the Canton of Zurich's own Staatsarchiv on Winterthurerstrasse updated its digital preservation policy in early 2025 to require deduplication checks as part of any new ingest workflow.

What Needs to Happen Next

Specialists in digital preservation broadly agree on the technical fix: implement hash-based deduplication at the point of ingest rather than retrospectively. The harder part is institutional. Zurich's cultural sector is fragmented across municipal, cantonal and federal funding lines, and systems rarely talk to each other. A photograph held by the Stadtarchiv, a copy lodged with the Baugeschichtliches Archiv, and a third instance in a university repository may each carry different rights annotations and catalogue numbers, making automated merging legally complicated even when technically straightforward.

The Swiss Federal Archives in Bern have signalled interest in developing shared standards, and a working group under the umbrella of Memoriav — the Swiss association for the preservation of audiovisual heritage, headquartered in Bern — is expected to produce guidance before the end of 2026. Whether Zurich's institutions move ahead of that timeline or wait for national-level coordination is, at this point, an open question among the professionals involved.

For ordinary users of Zurich's digital heritage platforms, the practical advice is simple: if a search returns what appears to be the same image listed under different catalogue numbers, it probably is. Reporting the discrepancy through each institution's feedback tool is the most direct way to flag it for manual review. Stadtarchiv Zürich, for its part, accepts corrections via its online contact form and has committed to processing them as part of routine cataloguing maintenance.