id = '/images/category/category2/category3/category4/';
var result = id.match(/^\/[a-z0-9_-]+\/[a-z0-9_-]+\/[a-z0-9_-]+\/[a-z0-9_-]+\/[a-z0-9_-]+\/$/);
alert(result);
result = id.match('^\/[a-z0-9_-]+\/[a-z0-9_-]+\/[a-z0-9_-]+\/[a-z0-9_-]+\/[a-z0-9_-]+\/$');
alert(result);