I did not notice the head/cut section ... anyway I have tested it , and the problem appears to be in Net::SMTP::TLS Module (it does replace line-ends and go into a while loop) which causes the image to get attached more than one time and get corrupted

Anyway, Here's a working code using Net::SMTP::SSL instead

use Net::SMTP::SSL;
my $mailer = Net::SMTP::SSL->new(
    Host    => 'smtp.gmail.com',    
    Port    => 465,
    Debug   => 1,
); 

$mailer->auth('username',  'password' );

$mailer->mail('username@gmail.com');
$mailer->to('somewhere@gmail.com');  
$mailer->data;  
$mailer->datasend($data_send);  
$mailer->dataend;  
$mailer->quit;
[download]

The beginning of your old code should be left intact.