Last week, the US Patent and Trademark Office published a series of minor Apple iPhone/iOS patents including a method of altering audio output from an electronic device based on image data.
If Apple develops an application based on the method described, you'll be able to modify your music using one or more characteristics in any image that's on the screen of your iPhone or iPod -- sharpness, brightness, motion, magnification, zoom setting, and so forth, as well as variation in any of the preceding characteristics.
Alternatively, the algorithm will also allow for producing audio, "wherein at least one characteristic of the audio output is determined based on one or more of the image data characteristics." In this case the image acts as a spectrogram that generates an audio signal. Whatever the result, it'd need to be appealing or the functionality is D.O.A.
New Scientist's Paul Marks notes that it's not just photos that could be used to modify the audio, but also your GPS position or motioned sensed in the accelerometers. He writes, "So being in a certain place could play back a version of a tune unique to that position, or jogging could activate a triple-tempo Ramones track to get obsessive gym bunnies into the cardio clinic all the sooner."
Below is a block diagram depicting the processing of image data and the alteration of an audio signal by components of an electronic device as described in the patent.