Zurich's Digital Archives Are Full of Duplicate Images — and Officials, Experts Are Divided on How to Fix It

Zurich's public institutions are sitting on millions of duplicate digital images, and the question of what to do about them has moved from the back offices of IT departments into a sharper civic debate. City archivists, university librarians, and software specialists say the problem is real, expensive, and increasingly urgent — but they disagree, sometimes sharply, on the right remedy.

The issue surfaced publicly this spring when the Stadtarchiv Zürich, housed on Alfred-Escher-Strasse, disclosed as part of its annual digitisation review that a significant share of its growing digital photograph collection contained redundant files — near-identical frames from the same shoot, re-scanned prints, or multiple format versions of a single image stored without coordination across departments. The archive has not released a precise figure, but the review, covering work done since 2021, described the duplication problem as a recurring obstacle to both storage efficiency and meaningful public access.

What the Experts Are Saying

At ETH Zurich, researchers in the university's Data Management Services group have been developing automated detection tools that use perceptual hashing — a technique that generates a short fingerprint for each image based on visual content rather than file metadata — to flag likely duplicates before a human archivist reviews them. Staff working on the project have described the approach in published documentation as faster and more consistent than manual sorting, though they caution that the technology cannot reliably distinguish between an intentional variant and an accidental duplicate without human judgment in the final step.

That caveat matters. At the Kunsthaus Zürich on Heimplatz, curators have long maintained that what looks like a duplicate to an algorithm can carry distinct provenance or condition information that makes it independently valuable. The museum's registrar department flagged this concern in internal discussions that were described to The Daily Zurich by a person with direct knowledge of those conversations, though that person was not authorised to speak on the record. The Kunsthaus declined to comment formally ahead of a broader policy discussion scheduled for later this month.

Zurich-based archival software company scope solutions AG, whose scope.Archiv platform is used by several cantonal institutions, has been marketing a deduplication module since early 2025. The company has presented the tool at events hosted by the Verein Schweizerischer Archivarinnen und Archivare — the Swiss association of archivists — arguing that automated replacement workflows can reduce storage costs significantly for mid-sized municipal archives. Independent assessors have not yet published a formal evaluation of those claims.

The Cost and Policy Questions

Storage is not cheap. Industry pricing for enterprise archival-grade cold storage in Switzerland runs broadly in the range of CHF 0.02 to CHF 0.05 per gigabyte per month for large institutional contracts, though exact figures vary by provider and volume. For institutions holding tens of millions of high-resolution image files, the cumulative cost across a five-year plan is substantial enough to attract the attention of the city's Finanzdepartement, which has been reviewing digital infrastructure spending across municipal bodies since the 2024 budget cycle.

The cantonal government has not yet issued formal guidance on duplicate-image management, but the Staatskanzlei Zürich confirmed in March that a working group examining digital asset governance more broadly was expected to produce recommendations before the end of 2026. Whether those recommendations will include binding rules on image deduplication — or leave it to individual institutions — remains an open question inside that process.

Direct democracy adds a layer of complexity. Any policy that involves the permanent deletion of publicly funded archival material could, in principle, trigger a political challenge, particularly if residents or cultural organisations argue that material is being lost without adequate consultation. Zürich's initiative and referendum mechanisms have been used before to contest digitisation and disposal decisions at the city level, and archivists say they are aware of that risk.

For now, institutions are being advised by the Swiss Federal Archives in Bern to document their deduplication decisions at the workflow level, creating an audit trail that can demonstrate which files were retained, which were flagged as redundant, and on what basis. That guidance stops short of a mandate, but specialists working with multiple Zurich-area clients describe it as the emerging professional standard — one that is likely to shape whatever the cantonal working group eventually proposes.