How do I get the full URL to an image in Cakephp?

Look inside the source code of HtmlHelper::image() to see how this helper creates the right URL; Slightly modified, this is how it's achieved:

$imageUrl = $this->assetUrl('image.jpg', array(
    // note: only required if you need the
    // URL -including- http://example.com
    'fullBase'   => true,
    'pathPrefix' => IMAGES_URL
));

The source code for Helper::assetUrl() can be found here: https://github.com/cakephp/cakephp/blob/2.3.2/lib/Cake/View/Helper.php#L305

After trying the various CakePHP global constants (ROOT, WEBROOT_DIR, WWW_ROOT, CSS, etc.) with no results, the general solution seems to be found in the $this->webroot property that returns the path to the application webroot. Thus for the various cases above we may have in our layouts, views or elements:

A simple image tag:

<img src="<?php echo $this->webroot; ?>img/foo.gif" .../ > 

A background image within a table cell the old way:

<td background="<?php echo $this->webroot; ?>img/foo.gif"> 

An input of type="image":

<input type="image" src="<?php echo $this->webroot; ?>img/go_btn.gif" ... /> 

I think webroot always work