1) Login to your blogger dashboard click on template and then click on edit html
2) Please download the copy of your template
3) check expand widget template checkbox
4) use Ctrl+F and find ]]></b:skin> 
5) Copy the codes given below and paste these codes just before it ]]></b:skin>

.zoomeffect img{-webkit-transform:scale(0.8);-moz-transform:scale(0.8);-o-transform:scale(0.8);-webkit-transition-duration: 0.5s;-moz-transition-duration: 0.5s;-o-transition-duration: 0.5s;opacity: 0.7;margin: 0 10px 5px 0;}
.zoomeffect img:hover{-webkit-transform:scale(1.1);-moz-transform:scale(1.1);-o-transform:scale(1.1);opacity: 1;
}

Finally click on save template your setting have ready



How To Activate Zoom Effect On Images Of Blogger BLOG
1) When you create a new post then click on Html
and change the class to "zoomeffect|
Example
your image class in post editor will be <div class="seperator" now change it into <div class="zoomeffect"

if you want to adding any other part of blogger you can use the following codes

<a class="zoomeffect" href="YOUR-IMAGE-URL/" target="_blank">
<img src="http://YOUR-IMAGE-URL" /></a>

Replace YOUR-IMAGE-URL with the link of image you want to apply for