Hey mooeena! I just looked at your game, and the problem is almost certainly that your image file is actually named "a.JPG", but you're referring to it as "a.jpg". Changing it fixes it:
Hey mooeena! I just looked at your game, and the problem is almost certainly that your image file is actually named "a.JPG", but you're referring to it as "a.jpg". Changing it fixes it: