#! perl -slw
use strict;
use GD;

sub rgba2n { unpack 'N', pack 'C4', pop, @_ }

my $src = GD::Image->newFromJpeg( $ARGV[0], 1 ) or die $!;

my $dia = $src->width < $src->height ? $src->width : $src->height;
my $maxDia = sqrt( $src->width**2 + $src->height**2 );
my $thickness = 10;

my $alpha = 127;
my $alphaDelta = $thickness * 127 / ( $maxDia - $dia );

$src->setThickness( $thickness );

while ( $dia < $maxDia ) {
    $src->ellipse(
            $src->width / 2, $src->height /2,
            $dia, $dia, rgba2n( 0, 0, 0, $alpha )
    );
    $alpha  -= $alphaDelta;
    $dia += $thickness;
}

open PNG, '>:raw', "vigged.png";
print PNG $src->png;
close PNG;

## Look at the result; starts default image editor.
system 'vigged.png';