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Check a photo's perspective and shadows for signs of AI

Real photos obey perspective: parallel lines meet at one point, and so do shadow lines in sunlight. Here's how to test a viral picture yourself.

By Alan Brown

Video cover: A 600-year-old art trick can expose AI fake photos

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📐 A 600-year-old art trick can expose AI fake photos.

🛤️ In a real photo, parallel lines like floor tiles, rail tracks and road edges all meet at one vanishing point.
☀️ Shadows work the same way: draw a line from an object to its shadow and in real sunlight every line meets at one point.
🤖 AI doesn't draw lines. It predicts pixels. Extend the lines in a fake and they miss.
🔬 It's the method Hany Farid, Berkeley's "godfather of digital forensics", uses, as covered in Science magazine's "Reality Check" by Kai Kupferschmidt: www.ischool.berkeley.edu/news/2026/science-magazine-highlights-prof-hany-farids-deepfake-detection-efforts
🖼️ Credits (Wikimedia Commons): Sather Tower – Coolcaesar (CC BY-SA 4.0); railway – PinchyCC (CC BY 4.0); road – W.carter (CC BY-SA 4.0); gallery floor – Jorge Royan (CC BY-SA 3.0); tree shadow – temporalata (CC BY-SA 2.0); printing presses – Harrison Keely (CC BY 4.0); newspaper press – Vanuatu Daily Post (CC BY 3.0); UC Berkeley aerial – UC Berkeley (CC BY 3.0); train driver's view – European Train Driver (CC BY 3.0); newsroom – Daily Nebraskan (CC BY 3.0). Perugino painting public domain; corridor and AI-generated city images CC0.

Context & limitations

Save this before the next viral "photo" hits your feed. Geometry is one clue, not proof on its own, and the prompt below walks you through the check.

Do this yourself

Help me check whether a photo might be AI-generated or edited, using perspective and shadow geometry. I'll attach the image. Where I found it: ___ . Go one step at a time and wait for me after each step. 1. Describe what's in the photo, and list every set of lines that should be parallel in real life (floor tiles, rail tracks, road edges, window frames, shelves). 2. For each set, tell me where to draw lines and whether they appear to meet at a single vanishing point. Say how confident you are, and why lens distortion or a cropped edge might make it look wrong. 3. If there are clear shadows in sunlight, tell me which object-to-shadow pairs to connect, and whether those lines appear to meet at one point. 4. Check anything else perspective can test: reflections, signs, text and repeated objects shrinking with distance. Then give me: - A short findings table: test, what you saw, consistent or inconsistent, confidence. - What a geometry check can't prove. A real photo can fail through distortion, and a fake can pass by luck. - Three non-geometry checks for this image: a reverse image search, the original uploader, and whether any trusted outlet has verified it. Don't call the photo real or fake from geometry alone. Say what the evidence suggests and what to check next.

Needs an AI that can read images. A geometry check is one clue, not a verdict, so the prompt keeps it alongside source and context checks.

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