For those who would like to show pictures in an image gallery, here's a gallery made with JavaScript and CSS that includes some thumbnails with which you will be able to pick different images on mouse click.
With the help of CSS, we can then place the <img> element to make it appear at the same position for each thumb and we'll be able to style the thumbnails as small blocks with a defined height/width. The script will add a click-event for each <li> object that changes it's child's <img> visibility and assigns an "active" class name to the <li>.

Step 1. Log in to your Blogger dashboard, go to Template > Edit HTML
Step 3. Inside the search box type </head> and click enter to find it.
  

 Style 2

<style type='text/css'>
#image-gallery { display: none; }
#jquery-gallery {padding:0;margin:0;list-style: none; width: 200px; }
#jquery-gallery li {background-size: 100%;-webkit-background-size: cover;-moz-background-size: cover; -o-background-size: cover;background-size: cover;margin-right: 10px; width: 80px; height: 80px; border: 3px solid #fff; outline: 1px solid #ddd; margin-right: 10px; margin-bottom: 10px; opacity: .5;filter:alpha(opacity=50); float: left; display: block; }
#jquery-gallery li img { position: absolute; top: 0px; left: 200px; display: none; }
#jquery-gallery li.active img { display: block; width:370px; border: 3px solid #fff; outline: 1px solid #E3E3E3; }
#jquery-gallery li.active, #jquery-gallery li:hover { outline-color: #bbb; opacity: .99;filter:alpha(opacity=99);}
#gallery-caption {background: rgba(0, 0, 0, 0.3);color: #fff;font-size: 16px;font-weight: bold;text-transform: uppercase;margin: 0 -17px;position: absolute;right: 0;text-align: center;top: 3px;width: 370px;}
</style>

Note: The display: none; of the first ID (#image-gallery) is to prevent images appear with their actual size before they go inside the gallery container, this is while loading the code. In #jquery-gallery we have the width of the container for the thumbnails (200px), so that they display in two rows and for this we need to count the width of the thumbnail (80px) plus the margins between them. The left declaration of #jquery-gallery li img is to move the larger thumbnail that shows on mouse click so that it won't overlap with the smaller thumbnails.

Step 5. Paste the code that you copied earlier just bellow the </head> tag.

Step 6. Just above the same </head> tag, add this script:

<script type='text/javascript'>
//<![CDATA[
var gal = {
init : function() {
if (!document.getElementById || !document.createElement || !document.appendChild) return false;
if (document.getElementById('image-gallery')) document.getElementById('image-gallery').id = 'jquery-gallery';
var li = document.getElementById('jquery-gallery').getElementsByTagName('li');
li[0].className = 'active';
for (i=0; i<li.length; i++) {
li[i].style.backgroundImage = 'url(' + li[i].getElementsByTagName('img')[0].src + ')';
li[i].title = li[i].getElementsByTagName('img')[0].alt;
gal.addEvent(li[i],'click',function() {
var im = document.getElementById('jquery-gallery').getElementsByTagName('li');
for (j=0; j<im.length; j++) {
im[j].className = '';
}
this.className = 'active';
});
}
},
addEvent : function(obj, type, fn) {
if (obj.addEventListener) {
obj.addEventListener(type, fn, false);
}
else if (obj.attachEvent) {
obj["e"+type+fn] = fn;
obj[type+fn] = function() { obj["e"+type+fn]( window.event ); }
obj.attachEvent("on"+type, obj[type+fn]);
}
}
}
gal.addEvent(window,'load', function() {
gal.init();
});
//]]>
</script>

Basically what this script does is to look if there is any ID named "image-gallery" and get the different list items that may exist within it. These elements will be displayed as thumbnails and a function will decide what to do when they are clicked. So, each time we click on a thumbnail, the "active" class will be assigned and the thumbnail should be visible in a larger container.

Step 7. Save the changes by clicking on the Save template button.

And finally, here's the HTML code. This is a normal list with the image-gallery ID, enclosed within a DIV with a relative position to avoid side effects of other pre-existing positions.

Step 8. Paste the below HTML to where you want to display the gallery by going either to Layout and adding a new gadget (click on the Add a gadget link and choose HTML/JavaScript), or inside a post or page within the HTML section.

<div style="position:relative;">
<ul id="image-gallery">
<li><img src="IMAGE-URL1" /></li>
<li><img src="IMAGE-URL2" /></li>
<li><img src="IMAGE-URL3" /></li>
<li><img src="IMAGE-URL4" /></li>
<li><img src="IMAGE-URL5" /></li>
</ul>
</div>

Note: if elements on your page overlap with this gallery, you might need to add the height declaration after the position: relative; The value of height depends on the size of your gallery.


Example:



Change IMAGE-URL1 with the image URL.

<div style="position:relative;">
<ul id="image-gallery">
<li><a href="page-URL"><img src="IMAGE-URL1" /></a></li>
<li><a href="page-URL"><img src="IMAGE-URL2" /></a></li>
<li><a href="page-URL"><img src="IMAGE-URL3" /></a></li>
<li><a href="page-URL"><img src="IMAGE-URL4" /></a></li>
<li><a href="page-URL"><img src="IMAGE-URL5" /></a></li>
</ul>
</div>


Here you need to replace the page-URL text with the URL of your page/post
Few tips:

To add space for more rows, increase the 100px value from this line:
#jquery-gallery li img { position: absolute; top: 100px; left: 0px; display: none;}

Save your widget and Happy Blogging.