Having just read the documentation for GraphViz.pm I don't see anything technically wrong with the portion of your code that deals with GraphViz.pm. There *is* one thing, but it's commented out: The documentation for GraphViz doesn't make any mention of _as_debug being a valid method. But as I mentioned, that's commented out, so I don't see that as the issue.

However, the documentation does show a completely different way of outputting the image (besides print). Out of curiosity, what happens if you use one of the other output constructs recommended:

$g->as_jpeg(\*STDOUT);
[download]

...immediately following your binmode call?

As a last resort, comment out your "print "content-type: image/jpeg\n\n";", and instead, output a 'text/html' header at the top of the program. Then put a 'print "Just completed add_node('london'....";' after each GraphViz method call to see which call in particular is causing the "hang".

Update: Ugh, how could I have missed seeing that the shebang line is wrong? I didn't even look at it. PodMaster++ for spotting it.