@Mix Android
No prior experience with this feature or scale, but Graphviz can embed images in the graph nodes it lays out. Write a script that converts your graph into a corresponding DOT (the input language for graphviz) file and places the images in the file system, then invoke graphviz.

Graphviz should handle that scale, and is quite flexible (raster graphics, svg, pdf all work, several layout engines to choose from).