There too many parameters of this shorcode. You can find detailed instructions on the documentation file. Here are some examples;
Auto thumbnail, lightbox, left align
[line]
[auto_thumb width="300" height="100" link="" lightbox="" align="left" title="" alt="" iframe=""]
http://rttheme12.templatemints.com/wp-content/uploads/2010/09/4b.jpg
[/auto_thumb]
[show_shortcode]
[auto_thumb width="300" height="100" link="" lightbox="" align="left" title="" alt="" iframe=""]
full path of your image
[/auto_thumb]
[/show_shortcode]
[line]
Auto thumbnail, link to a video, lightbox, right align
[line]
[auto_thumb width="300" height="100" link="http://vimeo.com/8245346" lightbox="" align="right" title="" alt="" iframe=""]
http://rttheme12.templatemints.com/wp-content/uploads/2010/09/4b.jpg
[/auto_thumb]
[show_shortcode]
[auto_thumb width="300" height="100" link="http://vimeo.com/8245346" lightbox="" align="right" title="" alt="" iframe=""]
full path of your image
[/auto_thumb]
[/show_shortcode]
[line]
Auto thumbnail, link to an external url, lightbox, center align
[line]
[auto_thumb width="300" height="100" link="http://google.com" lightbox="" align="center" title="" alt="" iframe="true"]
http://rttheme12.templatemints.com/wp-content/uploads/2010/09/4b.jpg
[/auto_thumb]
[show_shortcode]
[auto_thumb width="300" height="100" link="http://google.com" lightbox="" align="center" title="" alt="" iframe="true"]
full path of your image
[/auto_thumb]
[/show_shortcode]