www.metastatic.org/source/gray2snd/

This is GRAY2SND, a utility that "converts" images to audio waves.

GRAY2SND works by mapping vertical pixels to an audio frequency, each
pixel's intensity as an amplitude, and generates waveforms for a short
duration for each column of pixels.

GRAY2SND requires the following software packages:

   * fftw-2.1.3
   * libsndfile-1.0.3
   * popt-1.6.3

Two methods for generating waveforms are currently implemented:
summation of sine waves and using the inverse Fourier transform.

The summation method assigns a frequency to each row of pixels in the
image, generates a sine wave for each of these frequencies, scales each
wave by the brightness of each pixel, then sums the result. The inverse
Fourier method also assigns a frequency to each row of pixels, but then
takes the intensity of each pixel to to create spectrum map, which is
then used as input to the inverse discrete Fourier transform, which
essentially turns this spectrum into a composite waveform.