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Three killers, three different failures. Compression degrades, crops delete, screenshots replace. Drag the sliders and watch a real perceptual-hash score move: the same triage signal investigators use.
Read the score correctly
Above 92: likely same image, mild processing. 78-92: edited copy, heavier path. Below 78: heavily transformed or different file.
None of those name a subscriber. Similarity is triage. Attribution needs a recovered ID plus your log.
Test at your real settings
Don't test at pristine q95 if your route ships at q72. Social feeds land near 70-82 after re-encode. Test there.
Screenshots are a new bitmap: new dimensions, new compression, stripped metadata. Always prefer the downloadable attachment.
The quality cliff
Similarity degrades gracefully, then falls off a cliff, usually between q60 and q45 for photographic content. Plot the curve above and find your image's cliff.
Fragile watermarks die well before the cliff: the photo still looks fine at q72 while the payload is already gone. Looking fine is not surviving.
Screenshots are a new photo
A screenshot re-rasterizes at screen resolution, applies its own compression, and strips every tag. It shares nothing with your file except the arrangement of colors.
Enable screenshot simulation above: it downsamples to 1080px first, then applies your destroyers. That ordering matters. Detail lost early never comes back.
JPEG versus WebP
Same quality number, different damage: WebP's sharper quantization kills some structures JPEG keeps, and vice versa. Never assume one test covers both.
Switch the format dropdown at identical settings. The score gap is the reason your method choice must name the format, not just 'compressed'.
Takeaways
- JPEG quality under ~70 visibly degrades fragile marks while the image still looks fine.
- A 10% crop can delete the exact pixels a fragile method trusted.
- Screenshots strip metadata and re-rasterize everything; always download the file.
Check yourself
Optional, local, instant. 0/2 answered.
- Similarity score is 95 after a re-encode. What does that prove?
- A 10% crop drops the verdict a tier. Why?
For your niche
Client re-exports at 'high quality' still re-quantize. Test at q85, not q95: Lightroom's 85 is where gentle damage starts.
Your route is the harshest: feed re-encode plus screenshot risk. Preset 'screenshot of post' is your baseline, not your worst case.
Flat vector-like art collapses differently: edges ringing at q60 while photos look fine. Plot the curve on your own style, not the sample.