Zurich's Digital Archives Are Full of Duplicate Images — and Officials Are Finally Talking About It

Zurich's public institutions are sitting on tens of thousands of duplicate digital images across fragmented databases — and the people responsible for managing those collections say the situation has become untenable. Archivists, information scientists and municipal officials have spent the past several months in a quiet but intensifying debate about how to fix it.

The issue sounds technical. It isn't. Duplicate images inflate storage costs, slow retrieval systems and, in some cases, mean that a single historically significant photograph of, say, the Langstrasse quarter or the old Sihlpost building appears in three separate catalogues under three different metadata tags — none of them talking to the others. When a researcher at the Zentralbibliothek Zürich on Zähringerplatz searches for documentation of a specific urban planning period, they may receive contradictory results drawn from the same original source file.

What the Experts Are Saying

Information management specialists at ETH Zurich, whose library system holds one of the largest scientific image repositories in the German-speaking world, have been developing automated deduplication tools as part of a broader digital infrastructure project. The work builds on research into perceptual hashing — a technique that identifies visually identical or near-identical images even when file names, formats or metadata differ. Faculty affiliated with the ETH Library's digital preservation unit have described the problem as systemic across Swiss cultural institutions, not unique to any single archive.

At the Stadtarchiv Zürich on Neumarkt, staff have acknowledged that the volume of digitised material added since 2020 — covering everything from building permits to civic event photography — has outpaced the institution's capacity to deduplicate on intake. The archive has been operating under a digitisation mandate tied to the city's broader smart-city strategy, which set an ambitious 2025 target for converting physical holdings. Meeting that target meant prioritising volume over the kind of quality-control checks that would catch duplicate entries before they are embedded in the catalogue.

The Zentralbibliothek, which manages a separate but overlapping photographic collection covering Zurich's history from the late 19th century onward, has been in discussions with the Stadtarchiv about shared deduplication protocols since at least early 2026. No formal agreement has been announced publicly, but both institutions are understood to be watching a pilot programme at the Schweizerisches Nationalmuseum — whose Zurich branch sits near Platzspitz park — that is testing AI-assisted image matching against a sample of roughly 40,000 digitised objects.

Why It Matters Beyond the Archive

The practical stakes extend well beyond researchers. The canton's school system, which supplies licensed image content to secondary schools across Zurich through a centralised digital platform, draws on some of the same institutional repositories. When duplicate images carry conflicting licensing metadata — a known consequence of ad hoc digitisation — teachers and students can inadvertently use material under the wrong terms. Swiss copyright law, updated in the revision that came into force in April 2020, places the compliance burden squarely on the institution making the material available.

Storage is a cost question too. Cloud infrastructure for the city's cultural data holdings runs through a framework contract negotiated by the Finanzdirektion des Kantons Zürich. While precise figures for image-specific storage are not publicly itemised, independent analysts who study Swiss municipal IT budgets note that redundant data across large public collections routinely adds between 15 and 25 percent to baseline storage expenditure — a range that, even at the lower end, represents a meaningful line item for institutions already operating under constrained Kulturfranken budgets.

The debate now is about who coordinates the fix. Some specialists argue the task belongs to the Kanton Zürich's Staatskanzlei, which oversees digital governance. Others want ETH Zurich to anchor a technical standards body that individual institutions can voluntarily join. A third camp, represented informally among younger archivists in the city, favours a bottom-up approach: open-source deduplication tools shared freely among the Stadtarchiv, Zentralbibliothek and cantonal museum network, with no single institution in the lead role.

A working group is expected to present preliminary recommendations to cantonal cultural officials before the end of September 2026. Until then, the duplicates accumulate — one redundant image of the Grossmünster at a time.