The helper will generate image urls with named params to get thumbnails or whatever else operation is wanted and a hashes the url.
The hash can be checked using the Imagine Component to avoid that people try to bring your page down by incrementing the size of a requested thumbnail to generate thousands of images on your server.
$url = $this->Imagine->url(
array(
'controller' => 'images',
'action' => 'display',
1
),
array(
'thumbnail' => array(
'width' => 200,
'height' => 150
)
)
);
echo $this->Html->image($url);