use strict; 
use warnings;

##</code><code>##

my %char_pics=(); # before the big loop
while(<DATAFILE>){
...
    foreach(@chars) {
	if(!$_ == "") { 
            if (exists $char_pics{$_}) {
                $img= $char_pics{$_};
            }
            else {
                $img=$pdf->image_png("/var/www/html/font_test/Pumpkins/$_.png");
                $char_pics{$_}= $img;
            }
            vr->image(...
...