Analog Protection System (APS)
  CopyGuard by Macrovision

  Prevents copy from VHS to DVD.  

  Adds a signal that causes the vcr to think the picture is too bright. 

  The recorder compensates thus greatly reducing the brightness of one
    or more colors.

  Many TVs do not have the circuitry to detect the added signal and so
    don't have a problem.  Some newer TVs do have problems with Macrovision.