Even though Hexo suports markdown, the current asset folders implmention is hacky at best.
It does not allow for additional fields. Without the asset_path or image tag your image will often not show up on the index page.
The following code will allow you to set properties and display the image on the index page
<img src="{% asset_path image_0.png %}" style="width: 90%;"/>
A better way would be to include the markdown file in the Asset Folder.