This worked like a charm for me. No plugins required.
My images are in a assets/images/slider
directory.
{% for image in site.static_files %}
{% if image.path contains 'images/slider' %}
<img src="https://stackoverflow.com/questions/17677094/{{ site.baseurl }}{{ image.path }}" alt="image" />
{% endif %}
{% endfor %}
The image.path contains 'images/slider'
makes sure that only images in that folder are inserted.
Further reading here and on jekylltalk.
Troubleshooting:
As mentioned in the comments, if you have trouble with this approach, you might want to try removing the indentations before the Tag.