HTML Image Gallery Not Showing Images

I recently put an image gallery slideshow on my website. I put all the images in and tested it on my browser and it works fine.

However, when I uploaded the website to my server, some of the images do not show up. Here is the code below. Images 1,4, and 6 show up fine. However, 2,3, and 5 do not show up at all. I am very confused by this. They worked when I tested them in my browser. Now that they are uploaded, its not working properly.

Image Sizes: 1: 124kb 2: 617 3: 668 4: 139 5: 1610 6: 830

Does anyone have any suggestions on what might be causing this?

Thanks in advance!

<center><h1>Gallery</h1></center>
<ul data-orbit data-options="timer_speed:99999; bullets:false;">
<li>
<img src="img/slider/slide1.jpg" />
<div class="orbit-caption">caption here...</div>
</li>
<li>
<img src="img/slider/slide2.jpg" />
<div class="orbit-caption">caption here...</div>
</li>
<li>
<img src="img/slider/slide3.jpg" />
<div class="orbit-caption">caption here...</div>
</li>
<li>
<img src="img/slider/slide4.jpg" />
<div class="orbit-caption">caption here...</div>
</li>
<li>
<img src="img/slider/slide5.jpg" />
<div class="orbit-caption">caption here...</div>
</li>
<li>
<img src="img/slider/slide6.jpg" />
<div class="orbit-caption">caption here...</div>
</li>