Hi Mark,
MetaSynth maps color to spatial orientation. Frequency is based on vertical placement of the pixels. The particular frequencies are determined by the tuning map -- there are many useful tuning maps built-in and several thousand more provided with the software that can be used as custom tunings.
You can find a presentation about how the Image Synth works at:
http://www.uisoftware.com/MetaSynth/videos
The Image Synth basics video is the one that describes the basics of how the Image Synth works.
To do what you would like to do with MetaSynth, you would need a program to convert the images so that color data in your raw image were translated to vertical position in the image that you would use in MetaSynth.
Best,
Edward