GeoINT CTF — Reflection
Challenge: https://geoint.ctf.uz/d64a540f-9539-457e-ae1e-632bdcd32267
Status: Solved and verified
Objective
Geolocate a photograph showing swans and gulls beside a broad river, then identify the precise point accepted by the challenge verifier.
Visual observations
The image showed:
- a wide, controlled urban river;
- many mute swans and black-headed gulls;
- an engineered bank made from riprap and sloping precast concrete steps;
- a low bridge in the background;
- leafless vegetation, suggesting a cool-season European scene.
These clues suggested a managed section of a major Central European river rather than a natural lake shore.
Finding the matching riverbank
Reverse-image and landmark research led to the Danube beside Handelskai and Millennium City / Millennium Tower in Vienna. A Wikimedia Commons photo sequence from the same bank was especially useful:
Wien Donau 2014-12-03 088 Höckerschwäne Cygnus olor Lachmöwen Larus ridibundus Stockenten Anas platyrhynchos.jpg
The sequence showed the same combination of birds, river engineering and shoreline geometry. Its embedded/map position was approximately:
48.241017, 16.388147
Submitting that point returned close, proving that the correct location was within a very small radius.
Final refinement
Small offsets were tested around the source-photo coordinate. Moving the latitude north by 0.0001° produced the accepted result:
48.241117, 16.388147 -> correct
The accepted area is the Danube riverbank/treppelweg beside Handelskai, below the Millennium City complex in Vienna.
Result
- Location: Danube riverbank beside Handelskai, Vienna, Austria
- Coordinates:
48.241117, 16.388147 - Verifier result:
status: correct - Flag:
CTF.UZ{v3ry_be4u71ful_vi3w}
Map: https://www.openstreetmap.org/?mlat=48.241117&mlon=16.388147#map=19/48.241117/16.388147
Reference
- Wikimedia Commons match:
https://commons.wikimedia.org/wiki/File:Wien_Donau_2014-12-03_088_H%C3%B6ckerschw%C3%A4ne_Cygnus_olor_Lachm%C3%B6wen_Larus_ridibundus_Stockenten_Anas_platyrhynchos.jpg
Lessons learned
- Shore construction can be more discriminating than the wildlife itself.
- A matching geotagged photo is a strong lead, but the CTF may use a nearby target rather than exactly the public photo coordinate.
- Once the verifier reports
close, use very small cardinal offsets and record every response.