To add a side border to an image, you just need to add some CSS codes into your image html codes.
1. Add Thick border:
Below is an image with no side border around it and with the following html codes:<img src=”http://yoursite.com/flowers.jpg” alt=”” width=”50″ height=”50″ />

To add a thick grey border around the image, insert the following CSS code as highlighted in bold below:
<img style=”border: 3px solid #ecf1ef” src=”http://yoursite.com/flowers.jpg” alt=”” width=”50″ height=”50″ />
The end result:

You can adjust the border thickness by changing the border pixels or the border color by changing the …