En sites/all/modules/imagecache/

function theme_imagecache($namespace, $path, $alt = '', $title = '', $attributes = NULL) {
$attributes = drupal_attributes($attributes);
$imagecache_path = file_create_url(file_directory_path() .'/imagecache/'. $namespace .'/'. $path);
return '';
}

En template.php

function renacal_imagecache($namespace, $path, $alt = '', $title = '', $attributes = NULL) {
$attributes = drupal_attributes($attributes);
$imagecache_path = file_create_url(file_directory_path() .'/imagecache/'. $namespace .'/'. $path);

if ($namespace=='image250x250') {

$imagen='';

}
else {

$imagen='';

}

return $imagen;
}