Delete images programmatically

Delete all images from a product's media gallery programmatically:

Mage::app()->getStore()->setId(Mage_Core_Model_App::ADMIN_STORE_ID);

$mediaApi = Mage::getModel("catalog/product_attribute_media_api");
$mediaApiItems = $mediaApi->items($product_id);
foreach($mediaApiItems as $item) {
    $mediaApi->remove($product_id, $item['file']);
}