You have a couple of problems. You are creating a Photo object for each image...this is very inefficient. Second, you are packing a new button for each image, so the window grows downward. Also you don't need to declare use Tk::Photo, BUT you do need Tk::PNG or Tk::JPEG if you want them. Gif is included in Tk by default.

Here is how to do it. Note, you can also use a widget other than a button, and use the size getting methods of Tk::Photo to readjust the size of the display widget. It's kind of buggy when you have gifs of different sizes, and the widget(button) dosn't change size. But that would be a good learning exercise for you, to come up with a widget that can resize and center each image.

#!/usr/bin/perl
use warnings;
use strict;
use Tk;

my $mw    = new MainWindow;
$mw -> geometry ("820x780");
my @files = <*gif>;

# make one Photo object and one Button and reuse them.
my $shot = $mw->Photo(-file => "$files[0]"); #get first one
my $button = $mw->Button(-image => $shot)->pack();

for my $image (@files)
{
   $shot->blank; #clear out old image
   $shot->read($image);
   $mw->update;
   select(undef, undef, undef, .1);
}
$mw->MainLoop;
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