You need to set the canvas' scrollregion to the size of the image (plus anything else on the canvas).

use strict;
use Tk;
my $mw = MainWindow->new;
my $mycanvas = $mw->Scrolled(
  "Canvas",
  -width=>800,
  -height=>600,
  -scrollregion => [0,0,1019,1600],
  -scrollbars=>'se'
)->pack(-expand => 1, -fill => 'both');

my $headerpicpath = '/some/path/image_1019_wide_1600_high.gif';
my $pic = $mw->Photo(-file=>$headerpicpath);

$mycanvas->createImage(0,0,-image=>$pic,-anchor=>'nw');

MainLoop;
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