Istanbul's Duplicate Image Problem: How the City Stacks Up Against Rome, Barcelona and Beirut

Thousands of duplicate photographs — some identical, some near-identical — are clogging the digital archives of Istanbul's two largest municipal heritage bodies, creating a preservation headache that archivists say is slowing restoration work on some of the city's most at-risk structures. The problem sits at the intersection of rapid digitisation, underfunded metadata standards, and the sheer volume of imagery generated since Turkey's post-2023 earthquake audit of vulnerable buildings across the country.

The issue is not trivial. When field teams photographed structurally suspect buildings in Fatih, Beyoğlu and Üsküdar following the February 2023 Kahramanmaraş earthquakes, multiple agencies — including İstanbul Büyükşehir Belediyesi's (IBB) urban transformation directorate and the General Directorate of Foundations, which manages thousands of Ottoman-era structures — often dispatched independent teams to the same sites. The result was tens of thousands of overlapping image files, many without consistent geotag or timestamp data, dumped into separate institutional servers with no shared deduplication protocol.

A Global Problem With Local Consequences

Duplicate image management has become a recognised pressure point for heritage cities operating large-scale digitisation programmes. Rome's Soprintendenza Speciale encountered a similar bottleneck between 2019 and 2022 when it digitised roughly 1.4 million catalogue cards from the Fototeca Nazionale; the institution ultimately contracted a dedicated AI-assisted deduplication service to sort the backlog before it could migrate records to a unified national portal. Barcelona's Institut de Cultura ran into comparable issues digitising holdings from the Arxiu Fotogràfic de Barcelona, eventually standardising on a hash-matching system that flagged near-duplicate images for human review before ingestion.

Beirut's post-2020 port explosion documentation effort produced a cautionary example: multiple NGOs and municipal bodies photographed the same destroyed neighbourhoods in Mar Mikhael and Gemmayzeh independently, and the resulting archive fragmentation has, according to heritage professionals working in Lebanon, complicated insurance claims and restoration planning for years.

Istanbul's archivists are aware of these precedents. The IBB's BIMTAS technology subsidiary began piloting a deduplication layer for its GIS-linked photo database in early 2025, using perceptual hashing algorithms to cluster visually similar images before a human curator decides which version to keep. The pilot covered approximately 180,000 images from the Tarihi Yarımada — the historic peninsula bounded by the Golden Horn, the Bosphorus and the Sea of Marmara — and produced a shortlist for manual review within six weeks, according to a publicly available IBB project summary from March 2025.

Standards, Not Just Software

The harder challenge is institutional, not technical. The General Directorate of Foundations and the IBB do not share a common image metadata standard. Files arriving from one body may carry a property identifier in a format incompatible with the other's cataloguing system, meaning even a sophisticated deduplication engine can miss matches that a human would spot instantly. The Aga Khan Trust for Culture, which has been active in restoration work in the Zeyrek and Süleymaniye neighbourhoods, has noted the same metadata fragmentation when coordinating with Turkish state partners on documentation projects.

The cost of inaction is measurable. A 2024 report by the European Commission's JRC on digital heritage infrastructure across candidate and partner countries estimated that poor deduplication practices inflate long-term digital storage costs by 15 to 30 percent for institutions without active data governance programmes. For a city the size of Istanbul, running archives that now number in the tens of millions of images, that margin is not negligible against a municipal technology budget already stretched by lira depreciation.

What comes next depends partly on whether Istanbul's rival institutional cultures can agree on a shared standard before the next major digitisation push — the IBB has signalled plans to extend its building inventory survey to the Asian shore districts of Kadıköy and Maltepe through 2026. Heritage professionals watching the process suggest the BIMTAS pilot could serve as a proof of concept for a wider inter-agency protocol, provided the Foundations directorate agrees to participate. Institutions in other cities that have solved this problem — Rome most visibly — did so only after a senior political decision forced competing bodies to adopt a single ingest standard. In Istanbul, that decision has not yet been made.