Every Photo Remembers Being Saved: Double JPEG Compression Explained
Save a JPEG twice and the second save leaves a trace of the first. How double JPEG compression works, what it reveals, and why re-saved isn’t edited.
The EXIF thumbnail that gave the edit away
JPEG, WebP, PNG, HEIC, AVIF, and camera RAW files embed a firmware-generated thumbnail before any editing software has touched them. When software re-saves the image without updating the thumbnail, the mismatch is forensic evidence — one of 60+ forensic checks snapWONDERS runs automatically on every photo and video.
How to tell if a photo has been edited
How to tell if a photo has been edited: forensic analysis reads compression signatures, manufacturer metadata baselines, and thumbnail mismatches across JPEG, WebP, PNG, and video.