To get the base URL you can use this (would return "http:// localhost/yiistore2/upload")
Yii::app()->baseUrl
The following Code would return just "localhost/yiistore2/upload" without http[s]://
Yii::app()->getBaseUrl(true)
Or you could get the webroot path (would return "d:\wamp\www\yii2store")
Yii::getPathOfAlias('webroot')