[dktbs]

This isn't exactly related (as it doesn't produce a spectrogram), but the software pixivisor plays around with this idea: http://warmplace.ru/soft/pixivisor/

The software can act as a transmitter or receiver. In trasmitter mode, you can provide it a static image or animated gif, which it will convert into audio which plays continuously. In receiver mode, pixivisor listens via the mic or line-in (depending on hardware platform and whats attached) and reconstructs the image from the audio. You can then manipulate the audio however you want.

This demo uses a korg monotron's low pass filter and LFOs to mangle an animated gif of a cat: https://www.youtube.com/watch?t=63&v=g2W1W4fwEkg

Its really interesting to me to see how the audio modulation is represented in the receiver's output.