Abstract: The invention relates to an apparatus and method for enhancing the security of selected information associated with a negotiable document, such as the monetary value of a cheque. In the invention, one or more security features are printed or applied onto the cheque. One such security feature is an encrypted control code. The preferred embodiment employs a secret key cryptographic scheme to encrypt the monetary value and thereby generate a first control code which is printed on tile cheque. When the cheque is presented for payment, a validator, such as bank or cheque cle aring house, employs a verification system having a copy of the encryption key to read the monetary value from the cheque and re-encrypt it according to said scheme to generate a second control code. The cheque is not honoured if the first and second control codes are not identical. Another security feature is a security image, composed, for instance, from a foreground image of the monetary value superimposed over a background motif image.

Abstract: An enhanced scrambled video signal, method for making an enhanced scrambled video signal and apparatus for enhanced scrambling of a video signal are all characterized by a pattern added to a video signal. The pattern is formed from a pair of segments, including a black segment and a white segment which forms a high contrast transition therebetween. The transitions vary in horizontal location from one horizontal line to the next. The pattern causes an unauthorized television receiver to mistakenly lock onto the transitions in the pattern, as if the transitions represented horizontal sync signals, thus scrambling the video display. The apparatus for inserting the pattern may be formed by a sync detector, a video amplifier, a multiplexor and a control logic device. The video amplifier sets the video signal to a DC reference level. The sync detector detects the horizontal sync of the video signal which is sent from the video amplifier.

Abstract: A digital image is "watermarked", that is, authenticated by an embedded pattern. The pattern is created by hashing the image and adding a signature element. Manipulating this result by the seed for a random number generator leads to an initial two dimensional random black-and-white pattern. This pattern is manipulated by a cellular automaton and smoothed before being added to the original image. To determine whether the image is authentic, one retrieves the watermark by subtracting the watermarked image from the original to obtain the difference. The value of the correlation between the difference thus obtained and the smoothed pattern determines the presence or absence of the watermark.

Abstract: The invention relates to a method and apparatus for stack frame elimination for simple procedures with tail calls. Subject to certain prerequisite constraints, the invention modifies the procedure by converting all tail calls to direct branches. The code in the computer program for constructing and deconstructing the stack frame is eliminated. In a preferred embodiment of the invention, dead code elimination is performed on unreachable code. In an alternative, equally preferred embodiment, dead code is retained in the computer program.

Abstract: The present invention includes a method and apparatus for reducing the signal amplitude in long marks which are written into optical disks. When forming a long mark, an increased signal amplitude is typically caused by the blooming toward the end of the mark, and is often sensed by the focused spot in the adjacent track causing increased adjacent track crosstalk (ATC). However, when forming short marks, the effect of blooming is minimized. Therefore, by splitting a long mark into a sequence of short period marks, with short period spaces (1T) between each short period mark, the effect of blooming is substantially reduced.