<?xml version="1.0"?>
<config>
    <modules>
        <DigitalPianism_PixelTracking>
            <active>true</active>
            <codePool>local</codePool>
            <depends>
                <Mage_Checkout />
            </depends>
        </DigitalPianism_PixelTracking>
    </modules>
</config>

<?xml version="1.0"?>
<config>

    <modules>
        <DigitalPianism_PixelTracking>
            <version>0.0.1</version>
        </DigitalPianism_PixelTracking>
    </modules>

    <frontend>
        <layout>
            <updates>
                <pixeltracking module="DigitalPianism_PixelTracking">
                    <file>digitalpianism/pixeltracking.xml</file>
                </pixeltracking>
            </updates>
        </layout>
    </frontend>

    <global>
        <blocks>
            <pixeltracking>
                <class>DigitalPianism_PixelTracking_Block</class>
            </pixeltracking>
        </blocks>
        <helpers>
            <pixeltracking>
                <class>DigitalPianism_PixelTracking_Helper</class>
            </pixeltracking>
        </helpers>
    </global>

</config>

<?php

class DigitalPianism_PixelTracking_Helper_Data extends Mage_Core_Helper_Abstract
{
}

<?xml version="1.0"?>
<layout version="0.1.0">
    <checkout_onepage_success>
        <reference name="before_body_end">
            <block type="pixeltracking/tracker" name="pixeltracking" template="digitalpianism/pixeltracking/tracker.phtml"/>
        </reference>
    </checkout_onepage_success>
</layout>

<?php

class DigitalPianism_PixelTracking_Block_Tracker extends Mage_Core_Block_Template {

    protected $_lastOrderId;
    protected $_lastOrder;
    protected $_store;

    protected function _construct()
    {
        $this->_lastOrderId = Mage::getSingleton('checkout/session')->getLastRealOrderId();
        $this->_lastOrder = Mage::getModel('sales/order')->load($this->_lastOrderId);
        $this->_store = Mage::app()->getStore();
    }

    public function getLastOrder()
    {
         return $this->_lastOrder;
    }

    public function getLastOrderId()
    {
         return $this->_lastOrderId;
    }

    public function getOrderItems()
    {
         return $this->_lastOrder->getAllItems();
    }

    public function getCurrencyCode()
    {
         return $this->_store->getCurrentCurrencyCode();
    }
}

<?php

$lastOrderId = $this->getLastOrderId();
$lastOrder = $this->getLastOrder();
$orderItems = $this->getOrderItems();
$currency = $this->getCurrencyCode();

// Display your pixel tracker here