Markdown doesn't have a built-in way to add borders to images, but you can use HTML tags within Markdown to achieve this effect.

Workaround

Sample code

<img srce.jpg" alt="your-image-description" style="border: 2px solid  gray;">

Replace the image.jpg with your image URL and add the alt text for your image in place of "your-image-description"

You can adjust the border width, style, and color by modifying the style attribute as desired.

In the above sample code, we use the style attribute to add

Border width as 2-pixel
Border style as solid
Color of the border is set to gray

Shadow color

You can change the shadow color. Just replace "grey" with your desired color name. For example, blure, green, yellow, and more.
Gray has been used in the example because it is the most commonly used border color next to 'black'.

Outcome

Without border

1_Screenshot-without_shadow_Featured_image-Health_check_metrics.png

With border

2_Screenshot-with_shadow_Featured_image-Health_check_metrics.png