The image constraint token is a digital flag built into Blu-ray and HD-DVD discs that determines how those discs output video signals through the player’s output connectors. The goal of the image constraint token is to prevent unauthorized copies, or piracy, in high definition. An image constraint token works by instructing the player to downgrade Blu-ray and HD-DVD discs’ native high-resolution 1080p video to a standard-resolution 540p for output through its analog video connectors. The video signal from the player’s digital high-definition multimedia interface (HDMI) remains in full definition because HDMI output is copy-protected. The image constraint token is activated by the movie studio during the mastering process.
The image constraint token is a part of the Advanced Access Content System (AACS), an encryption scheme built into Blu-ray and HD-DVD discs with the goal of preventing piracy. The HDMI cables used on Blu-ray and HD-DVD players use High-Bandwidth Digital Content Protection (HDCP) to ensure that high-definition video can only be viewed on HDCP-enabled monitors. Blu-ray and HD-DVD discs and players use AACS and HDCP in conjunction with each other in an attempt to thwart piracy.
The image constraint token has become the source of much controversy because, while the token and copy-protected HDMI cables may help prevent pirated HD copies of movies, they may also prevent many consumers from seeing any improvement in image quality as they attempt to upgrade from DVD. Early adopters of HDTV sets who bought their displays before HDMI inputs were introduced will be forced to watch their new HD-DVDs in standard-definition.
More than three million Americans own HDTV sets that are inoperable with HDCP. Additionally, some forthcoming HD-DVD and Blu-ray players, such as the Microsoft Xbox 360 and base-model Sony PS3, will lack HDMI output - meaning that even if a consumer has a state-of-the-art HDTV, their new player will be unable to display high-definition video on discs with an activated image constraint token. This contradicts marketing claims of HD-DVD and Blu-ray technology as “future-proof”.
Adding to the controversy is the fact that the Federal Communications Commission approved HDCP in 2004, despite known flaws that researchers claim will result in the copy protection being broken 1-2 years after being introduced to the public. This means that the image constraint token might prevent consumers from watching HD video without serving its intended purpose. Movie studios such as Sony and Universal have promised not to activate the image constraint token for titles released in the first few years of HD-DVD and Blu-ray, to allow consumers time to switch to compatible hardware. Nevertheless, many consumers view the image constraint token as a hindrance.