How Prague's Duplicate Image Problem Grew From a Minor Annoyance Into a City-Wide Reckoning

Prague's municipal archive holds more than four million digital images. A significant share of them, according to a 2024 internal audit by the Prague Institute of Planning and Development, exist in duplicate or near-duplicate form — the direct result of at least three separate digitisation waves carried out without a common file-management standard. The city is now midway through a remediation programme that city hall launched formally in January 2026, and the question being asked in offices from Mariánské náměstí to Letná is a simple one: how did things get this bad?

The answer requires going back to the early 2000s. Prague's district offices began scanning paper records independently, each using whatever hardware and software was available at the time. The Old Town district office on Staroměstské náměstí ran one system; the Žižkov municipal office ran another. When the unified Prague eGovernment portal, Portál Pražana, was expanded between 2018 and 2021 to aggregate local records, engineers pulling material from these siloed stores found themselves importing images that already existed in the central repository — often in slightly different resolutions or colour profiles, meaning automated deduplication tools failed to flag them as matches.

Three Digitisation Waves, One Compounding Mess

The first wave of scanning, roughly 2002 to 2006, was paper-to-TIFF and largely uncoordinated. The second wave, pushed by an EU-funded modernisation grant under the Integrated Regional Operational Programme, ran from 2014 to 2017 and introduced JPEG compression for speed — creating files that were technically distinct from the earlier TIFFs even when depicting identical source material. A third and smaller wave in 2020 and 2021, driven by the pandemic-era push to digitise building permits and heritage documentation, added a further layer of redundancy, particularly for images tied to listed buildings in Malá Strana and Josefov.

Prague's Institute of Planning and Development, which sits at Vyšehradská 57, flagged the problem formally in its 2024 audit but noted that the scale had been informally known inside the city's IT directorate since at least 2019. The core complication is not storage cost, though cloud and on-premise hosting for the archive runs the city an estimated 8.4 million crowns annually according to budget documents published on the Prague City Hall transparency portal. The deeper problem is retrieval integrity. When planners working on projects in Holešovice or heritage officers reviewing applications in Hradčany pull photographic evidence from the archive, duplicate records can surface conflicting metadata — different dates, different authorship tags — attached to what is effectively the same image. That introduces avoidable uncertainty into decisions that carry legal weight.

What the Remediation Programme Actually Involves

The January 2026 programme, administered through the Department of Information Technology at Prague City Hall, uses a combination of perceptual hashing and human review. Perceptual hashing compares images by visual content rather than file properties, catching duplicates that differ only in compression or minor cropping. By April 2026, the first phase covering building-permit images from districts 1 through 5 had processed roughly 340,000 files, with around 18 percent flagged as probable duplicates pending human confirmation. District 1, which includes the Old Town and covers the densest concentration of heritage properties, generated the highest flag rate.

The second phase, covering districts 6 through 10 and including large amounts of urban planning photography from the Letná plateau redevelopment studies, is scheduled to complete by the end of October 2026. A third phase covering the outer districts is pencilled in for early 2027.

For Prague residents and professionals who interact with the archive — architects submitting planning applications, journalists filing freedom-of-information requests, historians working through the City Library on Mariánské náměstí — the practical advice is straightforward. When pulling images from the Portál Pražana or the physical archive at the New Town Hall, always record the unique document identifier attached to each file rather than relying on image filenames, which the audit found to be inconsistent across the three digitisation waves. City hall has published a one-page guidance note on the portal, updated in March 2026, explaining the new identifier format. Anyone who used archive images in official submissions before January 2026 and encounters a metadata discrepancy can request a reconciliation check through the IT department's dedicated helpdesk, which went live on 15 February.