There was a bug in certain Tk versions (I think 800.024 was among them) which caused not calling "binmode" internally on image files.

You may workaround the problem either by switching to a newer Perl/Tk version (I think both Tk800.025 and Tk804.027 should do), or use the -data option instead of the -file option to load the file. From memory, untested:

use MIME::Base64;
{
    local $/ = undef;
    open(my $fh, "image1.gif") or die;
    binmode $fh;
    $buf = <$fh>;
}
$mw->Photo("image1", -data => encode_base64($buf));
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