1.Login to your blogger dashboard--> layout- -> Edit HTML

2.Scroll down to where you see </head> tag .

3.Copy below code and paste it just before the </head> tag.

<style type='text/css'>
 
#outer-borders a img, #outer-borders a  { border: none; float: left; }
#outer-borders a { margin: 3px; }
#outer-borders a:hover { outline: 3px solid #0000ff; }
 
</style>

Note:You can change border color,outline size,margin,... But both outline size and margin must have a same numerical value.

4.Now add your images as below.

<div id="outer-borders">
   
<a href="#"><img src="https://1.bp.blogspot.com/_4HKUHirY_2U/SxIRWePfVYI/AAAAAAAAAZ8/MSmCLCmWA8k/slideshow+1+small.jpg" alt="#" /></a>
   
<a href="#"><img src="https://1.bp.blogspot.com/_4HKUHirY_2U/SxIRhli6o6I/AAAAAAAAAaM/fmkIOf7MPtE/slideshow+2+small.jpg" alt="#" /></a>
   
<a href="#"><img src="https://3.bp.blogspot.com/_4HKUHirY_2U/SxIRonaYyII/AAAAAAAAAac/ls3j_gSduPk/slideshow+3+small.jpg" alt="#" /></a>     
  
</div>

You are done.

Demo