You don't need a filehandle, rather you need to use the read statement. So rather than what you have here:

while(<$formdata{upload}>) {
  print;
}
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Change that to:

my $buffer;
while(read $formdata{upload},$buffer,1024) {
     print $buffer;
}
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you can also limit the size of the image being uploaded:

my $buffer;
my $max_size = 10 * 1024; # 10 KB but it can be whatever
my $size;
while(read $formdata{upload},$buffer,1024) {
     $size += 1024;
     if($size > $max_size) {
          print "Image is too big!";
          last;
     }
}
[download]