Here is a link to a description of an algorithm which seems promising:
http://cs.stackexchange.com/questions/12925/circle-packing-algorithm-used-by-percolator

To paraphrase:
Areas forbidden to circles would be masked out as black pixels.
For all white pixels, make a list of the distance from the white pixel to the nearest black pixel.
The list then contains the radius of the largest circle that could be placed at that pixel.
Process the list, (somehow), to add size constraints and some pseudo-randomization...
...write a MoI script...
- Brian