There are so many things you can do, like click with a mouse, and enter text at that position. Goo Canvas will even let you have rotated text. Like this, just load your pie chart image first(not shown):

#!/usr/bin/perl
use warnings;
use strict;
use Tk;
require Tk::DialogBox;


# right click on the canvas to pop a dialog
# to get text, the text will be placed on the canvas where you
# clicked, and will be draggable to desired position.
# canvases can be saved as postscript, then converted to
# whatever you want.

my $dx;
my $dy;
my $current;

my $mw = MainWindow->new;
$mw->geometry("700x600");

$mw->fontCreate('big',
   -family=>'arial',
  -weight=>'bold',
  -size=>int(-18*18/14));

my $canvas = $mw->Canvas(-width => 700, -height => 565,
                -bg => 'black',
        -borderwidth => 3, 
        -relief => 'sunken',
           )->pack;

my $closebutton = $mw->Button(-text => 'Exit', -command => sub{Tk::exi
+t(0)})
               ->pack; 


my $dialog = $mw->DialogBox(
    -buttons => [qw/Ok Cancel/],
    -title   => "Enter Text"
);

my $dialogT = $dialog->add("Text");
$dialogT->pack(qw/-padx 10 -pady 10/);


$canvas->bind('move', '<1>', sub {&mobileStart();});
$canvas->bind('move', '<B1-Motion>', sub {&mobileMove();});
$canvas->bind('move', '<ButtonRelease>', sub {&mobileStop();});

#right click to post text
$canvas->Tk::bind("<ButtonPress-3>", [\&getText, Ev('x'), Ev('y') ]);

MainLoop;

sub getText {
  # print "@_\n";
   my ($canv, $x, $y) = @_;
   my $x1 = $canv->canvasx($x);
   my $y1 = $canv->canvasx($y);
   print "$x1  $y1\n";

    $dialog->configure(-focus => $dialogT);
    $dialog->bind('<Return>' => undef);
  
  ## Determine whether or not the user hit "Ok"
    my $button = $dialog->Show();

    if ( $button eq "Ok" ) {
        my $letters = $dialogT->get( '1.0', 'end' );
        #print "$letters was submitted\n";
        $dialogT->delete( '1.0', 'end' );

        my $dragster = $canvas->createText( $x1, $y1, 
                             -fill => 'red',
                 -tags => ['move'],
                 -text => $letters,
                 -font => 'big',
                 -anchor => 'nw',
                 );
    
        $current = $dragster;
    }
}


sub mobileStart {
      my $ev = $canvas->XEvent;
      ($dx, $dy) = (0 - $ev->x, 0 - $ev->y);
      $canvas->raise('current');
      print "START MOVE->  $dx  $dy\n";
}


sub mobileMove {
      my $ev = $canvas->XEvent;
      $canvas->move('current', $ev->x + $dx, $ev->y +$dy);
      ($dx, $dy) = (0 - $ev->x, 0 - $ev->y);
      print "MOVING->  $dx  $dy\n";
}


sub mobileStop{

    $canvas->dtag($current,'move');

}
__END__
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From the doc for GD::stringFT():

"Another thing to watch out for is that successive lines of text should be separated by the "\r\n" characters, not just "\n"."