use strict;
my $str = '<p>Some text 1</p>
<p>Some text 2</p>
<p>Some text 3</p>';
my $regex = qr/((<p(.*?)>)([[:space:]]+?|.*?|[[:space:]]+?)(<\/p>)\s?){3}/p;
my $subst = '$0\\n\\t<img src="imagem.jpg">';
my $result = $str =~ s/$regex/$subst/rg;
print "The result of the substitution is' $result\n";
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Perl, please visit: http://perldoc.perl.org/perlre.html