Voice - is a free online soundscape synthesizer and sequencer. This Java applet allows you to draw your own 64 × 64, 16 grey-tone image and immediately hear the corresponding 64-voice polyphonic visual sound being synthesized on the fly! See and hear how The vOICe mapping works for your input. The 64-channel sound synthesis maps the image into an exponentially distributed frequency interval for a one second visual sound.
An interesting thing, though it is not easy to produce something well sounding.
On this animation page you can see how different images sound.