The problem is different depending on the version of GV.
With 2.8, only half of the node images are displayed, namely those inside HTML tables. The standalone ones declared through shapefile are not displayed at all (I checked the SVG serialization, they are not declared at all). But those that are displayed are correctly located w.r.t other elements in the graph. See  for a screen capture of the SVG rendering by ZGRViewer.
For comparison,  shows the correct output obtained by asking dot to generate a PNG image instead of an SVG document.
With 2.12, the SVG document contains all images, but as you can see in  there vertical coordinate is inverted. This is the ZGRViewer rendering. When I try to look at this SVG document in either Adobe Illustrator or Firefox, the images simply don't show at all.
The command lines used were :
dot -Tsvg input.dot -o output.svg dot -Tpng input.dot -o output.png
 http://www.lri.fr/~pietriga/2006/12/gv2_8_svg.png  HREF=http://www.lri.fr/~pietriga/2006/12/gv_2_8_png.png  http://www.lri.fr/~pietriga/2006/12/gv2_12_svg.png