Thank you man... I will update horde next week and try.

Implemented via a mime_drivers.php parameter.

Changes have been made in Git for this ticket:

Request #9129: Allow admin to define list of safe e-mail addresses 
that will not experience HTML image blocking

http://git.horde.org/diff.php/imp/config/mime_drivers.php.dist?rt=horde-git&r1=0106a25421134e74ab8cfc514492077d22c9dfc4&r2=0d3074deac715da0270637b4398536f6032e7024
http://git.horde.org/diff.php/imp/docs/CHANGES?rt=horde-git&r1=5a820898cfc8b88f235ae52cbc1de20081e04b52&r2=0d3074deac715da0270637b4398536f6032e7024
http://git.horde.org/diff.php/imp/lib/Mime/Viewer/Html.php?rt=horde-git&r1=a6d02a936008e877e0a4d5f615f5349709005451&r2=0d3074deac715da0270637b4398536f6032e7024

Every time when a new user comes in my system I send a welcome email 
with remote images (like promotional emails). It generates a problem 
due to all the images are blocked and user needs to click in "Show 
images"... I think that IMP might be able to read a global conf file 
of "allow emails" to always display remote images... I know the user 
can do it using html_image_addrbook, but in my point of view this list 
is a good global alternative to sysadm

Following is a stupid example of implementation..

In the file: imp/lib/Mime/Viewer/Html.php (line 247)

$headersshowimage = $this->_params['contents']->getHeaderOb();
$fromshowimage = $headersshowimage->getValue('from');

if (!in_array($fromshowimage,$_GLOBAL['allowemails']))
{
if ($inline &&
             $GLOBALS['prefs']->getValue('html_image_replacement') &&
             preg_match($this->_img_regex, $this->_mimepart->getContents()) &&
             (!$GLOBALS['prefs']->getValue('html_image_addrbook') ||
              !$this->_inAddressBook())) {
             $data = preg_replace_callback($this->_img_regex, 
array($this, '_blockImages'), $data);

             $status[] = array(
                 'icon' => Horde::img('mime/image.png'),
                 'text' => array(
                     _("Images have been blocked to protect your privacy."),
                     Horde::link('#', '', 'unblockImageLink') . 
_("Show Images?") . '</a>'
                 )
             );
         }
}