The HTML syntax has no real way of loading a background image directly, for this you need to use style-sheets.

The answer is

$c = CGI->new();
push @page, $c->header;
push @page, $c->start_html( -style=>{-src=>'/style/st1.css'})
... yada ...
[download]

and in the file ..../style/st1.css you include the contents:

BODY {background-image: /dir/image.png}
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This is untested. I'm sitting in someone elses house, so doing this from memory. If neccessary, look at the www.w3c.org web site for details on stylesheets

-- Ian Stuart
A man depriving some poor village, somewhere, of a first-class idiot.