オフラインで見える写真がサーバーに入れてオンラインで見ると写真が見えなくなる

class=coverで指定している背景写真がオフラインでは見えるのに、オンラインでは見えなくなってしまう現象に悩まされています。サーバはエックスサーバーを使っています。コードのせいでしょうか？
かれこれ２日間悩んでいるのですが自己解決できず...HTML、CSS、サーバにお詳しい方、お知恵を拝借したくお手数ですがどうぞよろしくお願いします。

HTML
1<!DOCTYPE html>
2<html>
3<head>
4<title>TARO TEST TEST 1</title>
5<meta charset="UTF-8">
6<link rel="stylesheet" href="Question.css"> 
7</head>
8    
9<body>
10
11<div>
12<img src="img/cover.jpg" alt="cover" width="100%" height="Auto" class="cover">
13
14<div class="name">TARO TEST<br>TEST1
15</div>
16
17<div class="introduction">This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_.
18</div>
19<div class="footnote">Copyright © <?php echo date("Y"); ?> TEST TEST - All rights reserved.</div>
20</div>
21
22    
23<div class="oddnumber">
24  <h1>1. CONTENT</h1>
25       <p>This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_This is a test text_This is a test text.</p>     
26       <img src="img/Turkish.jpg"　alt="test example1" width="35%" height="auto" class=img2>
27</div>     
28    
29</body>
30</html>

CSS
1<style type="text/css">
2
3.cover{
4position:relative;
5z-index:2;
6background-position: center center;
7background-repeat: no-repeat;
8background-attachment: fixed;
9background-size: cover;
10background-color: #464646;
11}
12
13.name{
14position:absolute;
15color:tomato;
16font-size:45px;
17left:45px;
18top:45%;
19z-index:3;
20}
21
22.introduction{
23background-color:rgba(0,0,0,0.5);
24color:white;
25font-size:12px;
26height:auto;
27width:57%;    
28padding:60px 60px 60px 60px;
29text-align:left;
30position:absolute;
31bottom:150px;
32right:0px;
33z-index:4;
34}
35
36.footnote{
37position: absolute;
38bottom:0;
39z-index:5;
40background-color:black;
41font-size:12px;
42color:white;
43width:100vw;
44padding:20px;
45margin:0;
46text-align:center;
47}
48
49.oddnumber{
50text-align:center;
51margin:0px; 
52padding: 150px; 
53background-image: linear-gradient(To Bottom, #fdfcfb 0%, lightgrey 80%);
54z-index:1;
55}    
56
57img.img2{
58margin:10px;
59}
60
61body{
62padding:0;
63margin:0;
64}
65
66</style>