To resize an image in Jekyll Markdown without needing to embed HTML in your markdown document:
<!-- Markdown -->
![My Image](/path/to/image.png)
{:}
Immediately After the Regular Syntax<!-- Markdown -->
![My Image](/path/to/image.png){:}
:
With a single dimension:
<!-- Markdown -->
![My Image](/path/to/image.png){:width="100%"}
Or with both dimensions:
<!-- Markdown -->
![My Image](/path/to/image.png){:height="700px" width="400px"}