Perhaps the most common error comes from assuming that if an image is fractal, then any music derived from it in a methodical manner must also be fractal.
This idea may seem compelling at first and can produce interesting, if sometimes disconcerting, compositions. However, claiming that these compositions are fractal is something like claiming that a poem by Robert Frost, if transliterated using the Cyrillic alphabet, makes sense in Russian.
The problem is that a fractal object is fractal precisely because of the arrangement of its constituent elements.
Mapping pixel characteristics to classes of MIDI data deconstructs a 2-dimensional image into a series of sequences, each corresponding to one column or row of the graphic. Even if a more complicated algorithm is used to read the image, the original fractal structure is gone.
While it may be possible that some other fractal distribution arises, this is by no means guaranteed.
Here are two representative quotes from Web sites that promote "fractal" music.
"The fractal images are created with Fractint using parameters supplied by visitors to Don's U-draw facility, and the midi files derived from these fractals are sequenced by Don: 'The fractal image is imported into the shareware program ART SONG, which scans the image for the RGB values of selected pixels, then converts these values into MIDI output. The MIDI
file is then imported into a music sequencer, either Cakewalk and/or Orchestra Plus, where I try to identify and isolate melodic and rhythmic lines, reassign instruments, and put these lines or tracks together again in musically interesting ways. The creative work is largely in the sequencing.'"
(http://thinks.com/sounds/fractal.htm)
"What if you took the mathematics of Chaos Theory; which is what creates fractal graphics, and applied those same maths to Music? This is what we refer to as "Fractal Music"... taking the "mathematical feedback" of fractal equations and rather than mapping the results to the pixels on a computer screen... mapping the results to the many aspects that define the sound of music. The Results Can Be Astounding. ... Since the early Greeks it has been known that many aspects of Music are mathematical in nature. Fractals produce patterns somewhere between Order and Chaos, Randomness and Predictability, much like many naturally occuring processes and structures, Therefore - Fractal Music ..."
(http://www.fractal-vibes.com)
It is probably more accurate, and certainly more charitable, to describe this type of
music as simply being "fractal inspired."