This security is enforced through the High-bandwidth Digital Content Protection (HDCP) system, available on some devices which support DVI and HDMI video connections.
[1] If any components in the display chain do not support HDCP (such as a display connected to the player through analog connections like component, composite or S-Video) and the ICT flag is enabled, the player automatically reduces the high-definition video to the resolution of 960x540 pixels before outputting it.
The Image Constraint Token applies on a per disc basis, so that one movie title could have it enabled while another from a different studio could have it disabled.
Without content protection, users with the appropriate equipment could easily capture each and every frame of the film at its full resolution, effectively making a "perfect" copy.
Some HDTV early adopters object to the ICT flag because initial HDTVs did not incorporate HDCP support and thus, if this was activated, these individuals would not be able to enjoy high-definition video from such discs.