#!/usr/bin/perl
use warnings;
use strict;

use XML::LibXML;

my $input = '<image href = "images/cron1.png"><alt></alt></image>';
my $dom = 'XML::LibXML'->load_xml(string => $input);
for my $alt ($dom->findnodes('//image/alt[not(text())]')) {
    $alt->parentNode->removeChild($alt);
}
print $dom;

##</code><code>##

open file.xml ;
rm //image/alt[not(text())] ;
save :b ;