You can use XML::LibXML: 
#!/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;

[download]

or the less verbose wrapper XML::XSH2: 

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

[download]

map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

In reply to Re: Replace empty alt tag on <img> tag by choroba
in thread Replace empty alt tag on <img> tag by vlearner

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