Istanbul's Duplicate Image Problem: The Numbers Driving a City-Wide Digital Reckoning

More than 2.3 million duplicate image files are clogging the Istanbul Metropolitan Municipality's digital archive systems, according to internal assessments circulated among municipal IT departments this spring — a figure that has forced a reckoning with how Turkey's largest city stores, tags and retrieves the visual records underpinning everything from earthquake preparedness maps to UNESCO heritage documentation.

The timing is not accidental. Istanbul sits at the intersection of two urgent pressures. Post-2023 Kahramanmaraş earthquake reforms pushed every municipality in Turkey to digitise structural survey imagery at speed, flooding servers with unverified, often redundant files. Simultaneously, a tourism rebound — Istanbul welcomed a record 20.2 million foreign visitors in 2024, according to the Turkish Statistical Institute — has sent heritage platforms scrambling to maintain accurate, high-quality image libraries for sites from the Hagia Sophia to the Princes' Islands. When duplicates pile up unchecked, the wrong photograph of a cracked wall can be filed against the wrong building address, with consequences that go well beyond an embarrassed archivist.

Where the Redundancy Accumulates

Two institutions sit at the centre of the problem. The Istanbul Deprem Risk Azaltma ve İyileştirme Projesi — known by its acronym IDMP, the city's primary earthquake resilience programme — has logged structural images from more than 47,000 buildings across districts including Fatih, Zeytinburnu and Avcılar since 2023. Field teams frequently upload multiple near-identical frames per site, and without automated deduplication software running at the point of ingestion, the database has ballooned. A separate but overlapping issue affects the Atatürk Library's digitisation unit on Millet Caddesi in Beyazıt, where conservators working to catalogue Ottoman-era maps and architectural drawings have found that batch scanning across three contracted vendors produced duplication rates of roughly 34 percent across a 180,000-image tranche completed between January and October 2025.

The municipal tourism portal — Visit Istanbul, operated under the Istanbul Provincial Directorate of Culture and Tourism — faces a reputational dimension on top of the administrative one. Travel aggregators including Google Maps and Booking.com pull imagery from municipal open-data feeds. When the same photograph of the Galata Tower appears under four different metadata tags, third-party platforms display inconsistent or outdated images, undermining the very brand the city spends tens of millions of lira promoting annually.

What the Data Actually Shows

A deduplication audit commissioned by the Metropolitan Municipality and completed in March 2026 put concrete numbers to the problem for the first time. Of roughly 6.1 million images held across the city's primary urban planning and heritage databases, approximately 38 percent were identified as exact or near-exact duplicates — images sharing more than 95 percent pixel similarity. Storage costs for redundant files were estimated at 4.2 million Turkish lira per year in cloud hosting fees alone, at current contract rates with the municipality's Ankara-based provider. Eliminating confirmed duplicates could free roughly 14 terabytes of server capacity by the end of 2026, according to the audit's projections.

The IDMP alone accounts for an estimated 800,000 of those redundant files. Field surveyors working under time pressure after the 2023 disaster protocols were told to over-document rather than under-document — a defensible instinct in a seismic emergency that created a long-term data management headache. Zeytinburnu, one of the highest-risk districts for liquefaction, saw the highest per-building image duplication rate in the programme at 6.4 images per structural assessment on average, against a target of two.

The municipality has allocated funding for a machine-learning deduplication tool to be integrated into the IDMP server infrastructure by the fourth quarter of 2026. The Atatürk Library has already piloted a perceptual hashing system on a subset of 20,000 files — a technology that identifies visually similar images even when file names or metadata differ — and reported a 91 percent accuracy rate in flagging genuine duplicates without deleting unique historical material. If the pilot scales across the full archive, librarians estimate the manual review backlog could be cleared within 14 months. For Istanbul's earthquake engineers and heritage conservators alike, that deadline cannot come soon enough.