No, any way you slice it, you're taking a screenshot, but AFAIK, Tk exposes no API to retrieve said information.

http://search.cpan.org/grep?cpanid=SREZIC&release=Tk-804.030&string=pixel&i=1&n=1&C=0

update: well, it might be possible with Tk::WinPhoto on linux, but it doesn't expose

GetDesktopWindow http://search.cpan.org/grep?cpanid=SREZIC&release=Tk-804.030&string=desktop&i=1&n=1&C=0

So at the very least you'd need X11::GuiTest

Probably easiest to use Imager::Screenshot

See also Gtk2-screenshot, Tk Screen and Canvas Screenshots

This isn't a specific answer, but maybe it might give you some idea on which direction to go. Read the documentation for

#!/usr/bin/perl -l

use strict;
use warnings;
use Imager;
use Imager::Fill;
use Data::Dumper::Concise;

my $file = 'Screenshot.png';

my $img = Imager->new();
$img->open( file => $file, type => 'png' );

print "Image information: \n";
print "Width:                  ", $img->getwidth();
print "Height:                 ", $img->getheight();
print "Channels:               ", $img->getchannels();
print "Bits/Channel:           ", $img->bits();
print "Virtual:                ", $img->virtual() ? "Yes" : "No";

my $colorcount = $img->getcolorcount;
    print "Actual number of colors in image: ";
print defined($colorcount) ? $colorcount : ">512";
print "Type: ", $img->type();

if ($img->type eq 'direct' ) {
    print "Modifiable Channels: ";
    print join " ", map {
        ($img->getmask() & 1<<$_) ? $_ : ()
    } 0..$img->getchannels();
}

my(@rgbanames) = qw( red green blue alpha );
my $mask = $img->getmask();
for (0..$img->getchannels() - 1)  {
    print $rgbanames[$_] if $mask & 1<<$_;
}

my $color = $img->getpixel(x=>50, y=>70);
print Dumper($color);
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