How Zurich's Digital Archives Ended Up Full of the Same Image Twice: The Long Road to Duplicate Replacement

Zurich's public institutions are sitting on a quiet mess. Across municipal databases, university digital libraries and news archives, thousands of duplicate images — the same photograph stored under different file names, in different resolutions, sometimes with contradictory metadata — have accumulated over more than a decade of rushed digitisation projects and incompatible content management systems. The problem is not new. Fixing it, finally, is.

The issue surfaced publicly this spring when ETH Zurich's library services flagged a review of its digital asset infrastructure, noting that consolidating and de-duplicating visual records had become a priority ahead of a planned system migration. ETH Zurich, ranked among the world's top ten universities for science and technology, holds one of the largest academic image repositories in the German-speaking world. The scale of the duplication problem there is a useful mirror for what has happened more broadly across the city.

How the Duplication Built Up

The origins trace back to the late 2000s and early 2010s, when institutions across Zurich scrambled to digitise analogue collections. The Zentralbibliothek Zürich on Zähringerplatz, which holds cantonal and municipal archives stretching back centuries, ran multiple digitisation rounds using different scanning vendors and software platforms. Each round produced its own file-naming conventions. When records were later merged into unified databases, duplicates came with them — often undetected because automated matching tools of that era relied on exact file names rather than content recognition.

The same pattern repeated itself in newsrooms. Regional publishers consolidating editorial photo libraries after the wave of Swiss media mergers between 2015 and 2022 found that images had been uploaded to multiple systems by different desks, sometimes three or four times over. A single press photograph from a Bundesplatz event in Bern, for instance, might exist in a Zurich archive under four different accession numbers. Storage costs compound: cloud storage pricing for large image archives in Switzerland typically runs between CHF 0.02 and CHF 0.04 per gigabyte per month, meaning even modest duplication across a library of several million files generates measurable waste over years.

The UBS and Credit Suisse merger fallout added another layer. When Credit Suisse's internal communications and marketing archives were absorbed into UBS systems during the 2023-2024 integration, brand and photography teams on Zurich's Bahnhofstrasse corridor discovered that two large, separately maintained image libraries were now theoretically one — with no clean deduplication protocol in place. The result was a combined archive that corporate image managers described, in general terms, as unwieldy.

The Technical and Legal Tangle

Replacing duplicate images is not simply a matter of deleting the extra copies. Swiss data retention law, combined with cantonal archiving requirements, means institutions must be able to demonstrate chain of custody for official records. Deleting a file that was once cited in a published report or legal document — even if an identical copy exists under a different identifier — can create compliance gaps. This is why the Stadt Zürich's own digitisation office, operating under the Stadtarchiv on Neumarkt in the Altstadt district, has moved cautiously rather than running bulk automated purges.

The practical approach now gaining traction uses perceptual hashing — a technique that generates a fingerprint from image content rather than file metadata — to identify near-identical images regardless of resolution or file name. Several Swiss federal and cantonal institutions, including bodies connected to the Swiss Federal Archives in Bern, began piloting these tools in 2024. Zurich-based institutions have been watching those pilots closely.

For organisations now beginning deduplication projects, the practical advice from archivists is consistent: establish a canonical master record before deleting anything, update all internal citations to point to the master, and retain a deletion log for at least ten years under Swiss archiving norms. The Zentralbibliothek is expected to publish updated guidance on this process later in 2026. For smaller cultural organisations in Zurich — theatre archives, museum collections along Heimplatz, community media groups — that guidance will likely serve as the closest thing to a sector-wide standard they will get.