I try a solution: untested code ahead.

use IO::File;
my $fh = IO::File->new_tmpfile;

$image->Write(file => $fh);
seek($fh, 0, 0);
$ftpSession->put($fh, $filename);
[download]

The temporary file will be erased as you close it. It's in someway as it never existed and it's just useful to pass a filehandle to the Net::FTP put method instead of a scalar (that the method doesn't accept).

$|=$_="1g2i1u1l2i4e2n0k",map{print"\7",chop;select$,,$,,$,,$_/7}m{..}g