I made something like that, too, but it's not currently online and just a short derpy chip-ish tune anyway.. though the image I embedded was little heart shapes, and they went nicely with the music, so there's that haha.
The Analysis & Resynthesis Sound Spectrograph[1] is a really nifty tool that can convert spectrograms to audio files and vice versa, making tasks like this trivial. Sadly the developer has shifted development into a proprietary project, but the last release of ARSS still works and is a real hoot to play with.
MetaSynth is all about that, you can import visuals, draw over them, filter them and then go back to audio, MetaSynth is available since a very long time, it was first running on Mac OS 9. http://www.uisoftware.com/MetaSynth/index.php
Forgive my ignorance but does a spectrogram carry all the information necessary to reproduce the sound that generated it? For example, assuming I had the spectrogram of a song, could I play the song using it?
Yes, the FFT/STFT[1] is generally invertible, potentially subject to knowing the parameters it was generated with, or finding some reference markers in the original input you could use to derive them.
There's also the possibility the spectrographic image itself might be a lossy representation of the actual frequency domain data, in which case you won't get a perfect result back out. Probably recognisable though.
If I had time I'd do some flubbing with octave/scipy and demonstrate it, but alas, the margins of this weekend are too small, etc, etc.
The Discrete-Time Fourier Series is invertible. The problem is that for each pixel the Fourier series is a complex number and what is plotted is the magnitude (so the phase is not shown). Reconstructing a signal from only the magnitudes of the Fourier coefficients is ill-posed, i.e. there are multiple signals with the same Fourier coefficient magnitudes.
Still there is active research on reconstructing signals from only the Fourier magnitudes (under several assumptions). This is called the 'phase-retrieval problem'.
http://en.wikipedia.org/wiki/Phase_retrieval
Discovery? That face was planted intentionally by the artist, and the knowledge of its existence has been passed around fans since its original release.
