Screen replay detection

Catching a photo of a screen instead of a real document.

Someone might display an image of an ID on a monitor and photograph the monitor. Screen replay detection recognizes that the camera saw a screen and not a physical card.

Detection of moire, refresh banding, and reflectance artifacts indicating recapture of a display. Moire is the wavy interference pattern that appears when a camera films a screen's grid of pixels, and refresh banding is the set of dark stripes that appear when a camera's exposure does not line up with the screen's refresh rate.

A screen replay check works like this:

1. The system analyzes the captured image for patterns that a display produces.
2. It looks at how light reflects off the surface, since glass and plastic behave differently from paper.
3. It returns a result that says whether the capture came from a physical document or a screen.

Common signs of a screen recapture include:

• Moire patterns, which appear as ripples across the image.
• Banding and flicker, which show up as stripes or uneven brightness.
• Glare and reflections, which look like the sheen of glass.
• Pixel structure, which appears at close range as a grid.

Screen replay detection sits next to terms that are easy to mix up:

• Document liveness confirms that a document was captured live and in person, and screen replay detection is one signal that supports it.
• Presentation attack detection (PAD) catches fakes shown to the camera, including screens showing a face.
• Digital forgery is a fabricated document image that a replay attack might display.