As is, this captures a bitmap of the whole screen. Use "%{PrtScn}" for just the current window. Interpreting and manipulating the bitmap captured is over to you. You may find this document useful. The site's pretty damn useful too. Qudos to PodMaster for a reference to that some time back.

#! perl -slw
#use Win32::Bitmap;
use strict;
use Win32::GuiTest qw[SendKeys];
use Win32::Clipboard;

my $cb = Win32::Clipboard->new();

$cb->Empty();
SendKeys( "+{PRTSCR}" );
$cb->WaitForChange();

my $image = $cb->GetBitmap() or die 'No bitmap there';

print 'Total size:', length $image;
my %BMPinfo;
@BMPinfo{
    (
        '01UINT  type',                    #! 2
        '02DWORD size',                    #! 4
        '03UINT  Reserved1',            #! 2
        '04UINT  Reserved2',            #! 2
        '05DWORD Offset',                #! 4
        '06DWORD biSize',                #! 4
        '07LONG  biWidth',                #! 4
        '08LONG  biHeight',                #! 4
        '09WORD  biPlanes',                #! 2
        '10WORD  biBitCount',            #! 2
        '11DWORD biCompression',        #! 4
        '12DWORD biSizeImage',            #! 4
        '13LONG  biXPelsPerMeter',        #! 4
        '14LONG  biYPelsPerMeter',        #! 4
        '15DWORD biClrUsed',            #! 4
        '16DWORD biClrImportant',        #! 4
    )                                    #!54
} = unpack 'A2 L S S L L V V s s L L V V L L', substr $image, 0, 54;

printf '%23s : %s'.$/, $_, $BMPinfo{$_} 
    for sort keys %BMPinfo;
__END__
C:\test>231894
Total size:1572918
           01UINT  type : BM
           02DWORD size : 1572918
      03UINT  Reserved1 : 0
      04UINT  Reserved2 : 0
         05DWORD Offset : 54
         06DWORD biSize : 40
        07LONG  biWidth : 1024
       08LONG  biHeight : 768
       09WORD  biPlanes : 1
     10WORD  biBitCount : 16
  11DWORD biCompression : 3
    12DWORD biSizeImage : 1572864
13LONG  biXPelsPerMeter : 0
14LONG  biYPelsPerMeter : 0
      15DWORD biClrUsed : 0
 16DWORD biClrImportant : 0
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