Pb pour centrer image

$contenu.='<div class="conteneur-images">';
$contenu.='<div class="boxgrid captionfull">';
$contenu.='<img src="images/PE_2008/collier_blason1.png">';
$contenu.='<div class="cover boxcaption">';
$contenu.='<a href="http://www.nonsensesociety.com/2009/03/art-by-jarek-kubicki/" target="_BLANK"><h3>Femme</h3>';
//$contenu.='<p>Artist<br/><a href="http://www.nonsensesociety.com/2009/03/art-by-jarek-kubicki/" target="_BLANK">More Work</a></p>';
$contenu.='</div></div>';
$contenu.='<div class="boxgrid captionfull">';
$contenu.='<img src="images/Homme_2006/chapelet_obsidienne1.png">';
$contenu.='<div class="cover boxcaption">';
$contenu.='<a href="http://www.nonsensesociety.com/2009/03/art-by-jarek-kubicki/" target="_BLANK"><h3>Homme</h3>';
//$contenu.='<p>Artist<br/><a href="http://www.nonsensesociety.com/2009/03/art-by-jarek-kubicki/" target="_BLANK">More Work</a></p>';
$contenu.='</div></div></div>';

h3{ 
margin: 10px 10px 0 10px; 
color:#FFF; 
font:18pt Arial, sans-serif; 
letter-spacing:-1px; 
font-weight: bold;  
}

.conteneur-images{
width: 1024px;
height: 369px;
border: 1px solid blue;
}

.boxgrid{ 
width: 263px; 
height: 350px; 
margin:10px; 
float:left; 
background:#161613; 
border: solid 2px #8399AF; 
overflow: hidden; 
position: relative; 
border: none;
}

.boxgrid img{ 
position: absolute; 
top: 0; 
left: 0; 
border: 0; 
}

.boxgrid p{ 
padding: 0 10px; 
color:#afafaf; 
font-weight:bold; 
font:10pt "Lucida Grande", Arial, sans-serif; 
}
				
.boxcaption{ 
float: left; 
position: absolute; 
background: #000; 
height: 50px; 
width: 100%; 
opacity: .8; 
/* For IE 5-7 */
filter: progid:DXImageTransform.Microsoft.Alpha(Opacity=80);
/* For IE 8 */
-MS-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=80)";
}

.captionfull .boxcaption {
top: 350px;
left: 0;
}

.caption .boxcaption {
top: 220px;
left: 0;
}
				
h3 a{}