I am using your dvipng but I am getting ''page'' markers in the 4 corners.
This is my command line
dvipng -o test.png -T tight -D 120 -z 9 -bg transparent test.dvi
The dvi file was produced with Context and not Latex. The dvipng was taken
from the Miktex 2.5 distro. I am also getting some dvipng warnings
This is dvipng 1.8 Copyright 2002-2006 Jan-Ake Larsson
[1]
dvipng warning: at (35,91) unimplemented \special{ps: gsave currentpoint
currentpoint translate 1.0 1.0 scale neg exch neg exch translate}
dvipng warning: at (35,91) unimplemented \special{ps: currentfont
currentpoint grestore moveto setfont}