Zurich Archives Push to Eliminate Duplicate Images in City-Wide Digitisation Drive

Stadtarchiv Zürich confirmed this week that its ongoing duplicate-image-replacement project has processed more than 40,000 digitised records since the programme's expanded phase launched in January 2026, removing redundant files and replacing low-resolution scans with standardised archival masters. The work, coordinated across several institutions along the Limmat corridor, marks the most significant overhaul of the city's digital image infrastructure in over a decade.

The timing is deliberate. Zurich's cultural memory institutions have been under pressure since the Swiss Federal Council's 2024 digital heritage strategy set a deadline of December 2027 for cantonal archives to meet unified metadata and resolution standards. Duplicate images — often the result of multiple institutions independently scanning the same historical photographs, maps, or planning documents — bloat storage systems, create version-control confusion, and push up licensing costs. With cloud storage contracts up for renewal at several institutions in autumn 2026, trimming redundant assets now carries direct financial consequences.

Who Is Doing the Work — and Where

The project spans at least three anchor institutions. Stadtarchiv Zürich, based at Neumarkt 4 in the Altstadt, is handling civic and administrative photography going back to the late nineteenth century. The Zentralbibliothek Zürich, whose main reading rooms sit on Zähringerplatz, is managing printed-map duplicates and press-photography collections. A third strand runs through the Museum für Gestaltung on Ausstellungsstrasse in Zürich West, where duplicate product-design and exhibition images from the postwar period are being rationalised. All three are feeding cleaned records into the Swiss portal Archivportal Helvetia, which aggregates public-domain holdings from institutions across the confederation.

The method is largely automated at the first pass. Open-source perceptual-hashing tools compare image fingerprints and flag near-identical files for human review. Staff then decide whether to keep the highest-resolution version, merge metadata from both copies, or retire the file entirely. According to figures circulated at a June 30 working-group session — which The Daily Zurich reviewed — the automated pass flags roughly one duplicate for every eleven images scanned, a rate that archivists say is consistent with similar projects carried out by Bibliothèque nationale de France and the British Library in recent years.

What the Clean-Up Means for Researchers and the Public

For anyone who has tried to license a historical photograph of Zürichsee or pulled planning documents for a heritage property in Seefeld, the practical frustration of encountering multiple near-identical versions of the same image — each with slightly different metadata, resolution, and rights statements — is familiar. Duplicate records also slow search results on platforms like e-pics, ETH Zürich's image archive, which holds more than two million assets and regularly fields requests from architects, publishers, and academic researchers.

ETH Zürich's image archive team has been running a parallel deduplication exercise since March 2026, focusing specifically on aerial photography of the city taken between 1960 and 1990. That collection alone contained an estimated 6,800 duplicate or near-duplicate frames before the project began, according to internal documentation shared at the June 30 session.

Storage costs in Switzerland's archival sector are not trivial. Commercial cold-storage pricing for large cultural institutions currently runs at roughly CHF 0.02 to CHF 0.04 per gigabyte per month depending on contract terms and redundancy requirements — figures that accumulate quickly when collections run into the hundreds of terabytes.

The practical advice for researchers right now is to hold off on bulk downloads from Archivportal Helvetia until at least September 2026, when the first major tranche of cleaned and re-linked records is expected to go live. Institutions have warned that some persistent URLs for individual image records will change as duplicates are retired and canonical versions are assigned new stable identifiers. Bookmark searches rather than individual file links, and check back after the September refresh. Anyone with active licensing agreements covering historical Zurich imagery should contact the Stadtarchiv directly at Neumarkt 4 to confirm which version of a given image their contract references — before the old URLs disappear.