use warnings;
use strict;

use HTML::TreeBuilder;

my $str = "<a href ='some\\where'><img src='apple.gif'></img></a>";
my $root = HTML::TreeBuilder->new_from_content($str);

for ($root->look_down ('_tag', 'a')) {
    next if ! $_->look_down ('_tag', 'img');
    
    print $_->as_HTML ();
}
[download]

which prints:

<a href="some\where"><img src="apple.gif"></a>
[download]

should get you started. Take a look at HTML::TreeBuilder and HTML::Element.