...
use JSON;
use MIME::Base64;

my $ret_data = {
  'status' => 5, # success
  'message' => "here is the file $filename you asked"
  'message-html' => "<b>success blah blah for $fileame</b>",
  'data' => MIME::Base64::encode_base64($image_binary_data)
};
# if using CGI.pm
use CGI;
my $cgi = CGI->new;                  
print $cgi->header(-type => "application/json", -charset => "utf-8");
print JSON::encode_json($ret_data);

# or if using Mojolicious
$c->render(json => $ret_data);