You might want to look at one of the canvas type widgets, you can lay down an image on the canvas, then place a small icon on top and move it. Google for Tk::Zinc examples, see Goo Canvas and transparent images or look at this code, to see how canvases work

#!/usr/bin/perl
use warnings;
use strict;
use Gtk2 -init;
use Gnome2::Canvas;
use Glib qw(TRUE FALSE);

my $draw_flag = 0;
my %lines;   # way to store multiple continuous lines
my $count = 0;

my $window   = Gtk2::Window->new;
$window->signal_connect( destroy => sub { exit } );
$window->set_default_size( 500, 500 );

my $vbox = Gtk2::VBox->new;
$vbox->set_border_width(4);
$vbox->show;

my $hbox = Gtk2::HBox->new(FALSE, 4);
$vbox->pack_start($hbox, FALSE, FALSE, 0);
$hbox->show;

$window->add($vbox);

my $scroller = Gtk2::ScrolledWindow->new;
my $canvas   = Gnome2::Canvas->new();
my $white = Gtk2::Gdk::Color->new (0xFFFF,0xFFFF,0xFFFF);
$canvas->modify_bg('normal',$white);

$scroller->add( $canvas );
$vbox->pack_start($scroller, 1, 1, 0); 

$canvas->set_scroll_region( 0, 0, 700, 700 );
$window->show_all;

my $root = $canvas->root;

my $text = Gnome2::Canvas::Item->new(
    $root, 'Gnome2::Canvas::Text',
   x          => 20,
   y          => 15,
   fill_color => 'black',
   font       => 'Sans 14',
   anchor     => 'GTK_ANCHOR_NW',
   text       => 'Click to start and stop drawing....Drag Mouse'
);


$canvas->signal_connect (event => \&event_handler);

# Zoom
my $z = Gtk2::Label->new("Zoom:");
$hbox->pack_start($z, FALSE, FALSE, 0);
$z->show;

my $adj = Gtk2::Adjustment->new(1, 0.05, 100, 0.05, 0.5, 0.5);
my $sb = Gtk2::SpinButton->new($adj, 0, 2);
$adj->signal_connect("value-changed", \&zoom_changed, $canvas);
$sb->set_size_request(60, -1);
$hbox->pack_start($sb, FALSE, FALSE, 10);
$sb->show;

my $button1 = Gtk2::Button->new_from_stock('Screenshot');
$hbox->pack_start( $button1, FALSE, FALSE, 0 );
$button1->signal_connect( clicked => \&screenshot );


$window->show_all();

Gtk2->main;

##############################

sub event_handler{
     my ( $widget, $event ) = @_;
     #print $widget ,' ',$event->type,"\n";

     my $scale = $adj->get_value;
     # print "scale->$scale\n"; 

    if ( $event->type eq "button-press" ) {
        $draw_flag = 1;
         
        #start a new line curve
        $count++;
        
        my ($x,$y) = ($event->x,$event->y);
#        print "$x  $y\n";
        
        $lines{$count}{'points'} = [$x/$scale,$y/$scale,$x/$scale,$y/$
+scale]; #need at least 2 points 
        $lines{$count}{'line'} = Gnome2::Canvas::Item->new ($root,
        'Gnome2::Canvas::Line',
         points => $lines{$count}{'points'},
        fill_color => "red",
        width_units => 3.0,
        cap_style => 'projecting',
         join_style => 'miter',
            );
     }

    if ( $event->type eq "button-release" ) {
        $draw_flag = 0;
    }


    if ( $event->type eq "focus-change" ) {
        return 0;
    }
    
    if ( $event->type eq "expose" ) {
        return 0;
    }
    
    
  if($draw_flag){
    #left with motion-notify
    if ( $event->type eq "motion-notify"){
    my ($x,$y) = ($event->x,$event->y);
#    print "$x  $y\n";
 
     push @{$lines{$count}{'points'}},$x/$scale,$y/$scale;
     
     $lines{$count}{'line'}->set(points=>$lines{$count}{'points'});

#        my $p = $lines{$count}{'line'}->get('points');
#        print "@$p\n";
    }
  }        

}


sub zoom_changed {
    my ($adj, $canvas) = @_;
    $canvas->set_pixels_per_unit($adj->get_value);
}


sub screenshot{

#we are going to save the visible canvas
my ($width, $height) = $canvas->window->get_size;

# create blank pixbuf to hold the image
my $gdkpixbuf = Gtk2::Gdk::Pixbuf->new ('rgb',
                    0,
                    8,
                    $width,
                    $height);

$gdkpixbuf->get_from_drawable ($canvas->window, 
             undef, 0, 0, 0, 0, $width, $height);

#only jpeg and png is supported !!!! it's 'jpeg', not 'jpg'
$gdkpixbuf->save ("$0.jpg", 'jpeg', quality => 100);
return FALSE;
}

#$pixbuf->save ($filename, 'jpeg', quality => '100');
#  Currently only a few parameters exist.  JPEG images can be saved
#  with a "quality" parameter; its value should be in the range
#  [0,100].  Text chunks can be attached to PNG images by specifying
#  parameters of the form "tEXt::key", where key is an ASCII string of
#  length 1-79.  The values are UTF-8 encoded strings.  
__END__
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