I talk about this in my 'star generator' for IM Examples advanced
http://www.imagemagick.org/Usage/advanced/#stars
Also see a example of its use in...
http://www.imagemagick.org/Usage/anim_basics/
But the code for this has not been created. People however are welcome to try to do this and submit there scripts to add stars, or sparkles to a 'masked' area.
For finding masked areas, I have been looking at using
-segment (doesn't work properly) and reduced color sets...
-blur 0x3 +dither -color 3 from which the area to seed for stars can be pulled out, or user selected.
ASIDE: This method of finding 'areas' or image segments, is currently in development by my for the purposes for finding image metrics in comparing thousands of images. Basically because the current IM implementation of
-segment is so usless, and extremely slow.