[Plugin: CSV Importer] Help with Import containing Image URL Custom Field

I am trying to use this plugin to import to my fresh wordpress installation with this plugin installed.

My theme using a custom field…and the source of my Add New Post has this :

<input type=”hidden” name=”sp_nonce_name” id=”sp_nonce_name” value=”fcef7fb919″ /><label for=”_image_url”>Image URL:</label>
<input style=”width: 95%;” type=”text” name=”_image_url” value=”” />

</div>

What do I use as the header name so that CSV Importer plugin imports it into the correct format ?

http://wordpress.org/extend/plugins/csv-importer/