Exploring Hidden JPEG Features

Hackaday is reporting on an unexpected capability buried in the JPEG format's architecture. A developer discovered that JPEG's progressive loading mechanism—built to show a low-resolution draft before the full image data arrives—can be hacked to display two completely different images in sequence. The first image loads at low resolution, then the higher-resolution data replaces it with an entirely separate picture, creating a kind of one-way animation. The workaround is severely constrained: roughly nine frames maximum, and no way to encode timing information, so the sequence plays as fast as the internet allows. It's a clever exploit of how this decades-old format still dominates image compression on the web, and a reminder that even ancient standards can harbor surprises for anyone curious enough to dig.

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