问没有从crontab加载的kivy背景图像

EN

class MainScreen(Widget):
    res = True
    plastic = True
    paper = True 
    def __init__(self,**kwargs):
        super(MainScreen,self).__init__(**kwargs)
        self.animate()

class Warn(App):


    def build(self):
        return MainScreen()

<MainScreen>:
    FloatLayout:
        size: root.width, root.height
        canvas.before:
            Rectangle:
                pos: self.pos
                size: self.size
                source: "resources/bg.jpg"
        Label:
            text: "Do the thing"
            color: 0,0,0,0.8
            font_size: 100 
            pos_hint: {"center_x":0.50,"center_y":0.90}
        Label:
            text: "blabla" 
            font_size: 47   
            pos_hint: {"center_x":0.71,"center_y":0.37} 
        Image:
            id: img1
            source: "resources/img.jpg" 
            pos_hint: {"center_x":0.71,"center_y":0.50}