Copenhagen's Fight Against Duplicate Images in City Records: How It Stacks Up Against Amsterdam and Berlin

Copenhagen's Teknik- og Miljøforvaltningen — the city's technical and environmental administration — has been quietly running a deduplication sweep of its municipal image database since January 2026, targeting tens of thousands of redundant photographs that have accumulated across planning, heritage, and infrastructure departments over the past two decades. The effort, formally tied to the city's broader Digital Copenhagen 2025-2030 strategy, is the most systematic attempt the municipality has made to address a problem that has quietly inflated storage costs and slowed down public records requests for years.

The timing is not accidental. European cities that digitised large volumes of paper archives in the late 2000s and early 2010s are now hitting a wall. Those mass-scanning projects prioritised speed over rigour, and the result in many cases was the same image filed under multiple department codes, multiple project numbers, or both. In Copenhagen, the problem became acute enough that the city's own IT department flagged it as a drag on its cloud migration, which is scheduled for completion by the end of 2027.

What Copenhagen Is Actually Doing

The deduplication project is being run out of the Rådhuset on Rådhuspladsen, coordinating between at least four separate municipal departments. The city is using a combination of perceptual hashing — a method that identifies near-identical images even when file names differ — and manual review for photographs flagged as culturally or historically significant. The Copenhagen City Archive, Stadsarkivet, based in Ørestaden, is involved in sign-off for any image marked for permanent deletion rather than consolidation.

The scale is considerable. Municipal records reviewed by The Daily Copenhagen indicate the city's central image repository held more than 340,000 photographs as of a 2024 internal audit, with an estimated 18 to 22 percent flagged as probable duplicates. That figure puts the problem squarely in line with what other Northern European capitals have reported, though direct comparisons are complicated by differing definitions of what counts as a duplicate versus a legitimate variant image taken at a slightly different angle or time.

Amsterdam's Stadsarchief completed a similar deduplication exercise in 2023, reducing its active digital photograph count by roughly 14 percent and cutting associated cloud storage costs by an amount the archive described publicly as significant, without specifying a euro figure. Berlin's Landesarchiv has taken a more decentralised approach, delegating deduplication decisions to individual Bezirke — the city's administrative districts — which critics there say has produced inconsistent results across the 12 districts, with some moving quickly and others barely starting.

Where Copenhagen Pulls Ahead — and Where It Doesn't

Copenhagen's centralised sign-off requirement through Stadsarkivet gives it a structural advantage over Berlin's fragmented model. Any image touching a listed building, a planning application from before 1990, or a documented public event cannot be deleted without archival clearance. That rule, introduced specifically for this project, has slowed the process but reduced the risk of losing irreplaceable documentation of neighbourhoods like Nørrebro and Vesterbro, which underwent dramatic physical transformation in the 1970s and 1980s and whose photographic records carry significant historical weight.

Where the city lags is speed. Amsterdam finished its sweep in under 18 months. Copenhagen's project, which began in January 2026, is not expected to reach final sign-off before the third quarter of 2027. Officials at Teknik- og Miljøforvaltningen have not publicly explained the timeline gap, though the additional archival review layer is the most obvious factor.

For residents and businesses, the practical consequence is mainly felt when submitting records requests through the Aktindsigt system — the Danish public records access mechanism. Searches that return dozens of near-identical photographs still complicate requests, particularly for planning documents related to properties along streets like Amagerbrogade or in the Sydhavn development zone, where construction photography from multiple contractors was filed separately over many years.

The city has committed to publishing a progress report on the deduplication project by September 2026. Whether that report will include a clear storage cost figure — something Amsterdam provided and Berlin has so far not — will tell a lot about how seriously Copenhagen is treating public transparency around what is, at its core, a very unglamorous but genuinely consequential piece of urban administration.