title: WordPress simple Image Shortcode
body: <p>I am a newbie, please help me with creating a wordpress image shortcode, as simple as:</p>
  
  <pre><code>[img src=""]
  </code></pre>
  
  <p>Which shows its thumbnail (thumbnail width=100%), links to OR opens the same source image, when clicked.</p>
  
  <p>I tried searching but could not find in existing plugins, please guide me if any.</p>
  
  <p>Please guide me thoroughly for every copy paste in function.php or anywhere else.</p>