signature - Methods to Compute a Digital Signature for an Image

- NAME
- SYNOPSIS
- FUNCTION DESCRIPTIONS

- SignatureImage

# NAME

signature - Methods to Compute a Digital Signature for an Image

# SYNOPSIS

unsigned int SignatureImage( Image *image );

# FUNCTION DESCRIPTIONS

## SignatureImage

Method SignatureImage computes a digital signature from an image. This signature uniquely identifies the image and is convenient for determining if the colormap of a sequence of images is identical when animating. The digital signature is from RSA Data Security MD5 Digest Algorithm described in Internet draft [MD5], July 1992, computed on the pixels after expanding them to 64-bit RGBA representation, with the two bytes of each 16-bit sample ordered most significant byte first. The signature is in RGBA or CMYK order depending on the colorspace of the image. If the image does not have any alpha information, an opaque value (65535) is used.

The format of the SignatureImage method is:

> unsigned int SignatureImage ( Image *image );

A description of each parameter follows:

image:
  The address of a structure of type Image.