Sngine does not have profile default cover as of out of the box, so I added this little hack
Open profile.tpl look for content/themes/default/templates
<!-- cropped-cover -->
<img class="js_position-cover-cropped {if $user->_logged_in && $profile['user_cover_lightbox']}js_lightbox{/if}" data-init-position="{$profile['user_cover_position']}" data-id="{$profile['user_cover_id']}" data-image="{$profile['user_cover_full']}" data-context="album" src="{$profile['user_cover']}" alt="{$profile['name']}">
<!-- cropped-cover -->
And after that Add
{else}
<!-- Default cover image -->
<img class="js_position-cover-cropped" src="{$system['system_url']}/content/themes/{$system['theme']}/images/default_cover.jpg" alt="{__("Default Cover")}">
add a default cover image to theme folder like this
/content/themes/default/images/default_cover.jpg
and that is all enjoy.