Galery :probleme d'affichage

<div class="prev" onmousedown="scroll_left()"></div>
<div class="gallery_1">
<div class="photos" id="photos">
<?php
$sql="SELECT id_photo,extension FROM table_galery_2 ORDER BY timestamp ASC";
$db->query($sql);
$div="";
$i=0;
while($row=$db->fetch_array())
{
?>
<div id="photo_<?php echo $i; ?>">
<img src="GALERY_2/photo_<?php echo $row['id_photo']; ?>.<?php echo $row['extension']; ?>" height="135" width="auto" />
</div>
<?php
$i++;
}
?>
</div>
</div>
<div class="next" onmousedown="scroll_right()"></div>

div.content div.prev {
background-image: url('../GFXs/fleche_gauche_1.jpg');
width: 70px;
height: 135px;
float:left;
margin-right: 10px;
cursor: pointer;
}
div.content div.next {
background-image: url('../GFXs/fleche_droite_1.jpg');
width: 70px;
height: 135px;
float:left;
margin-left: 10px;
cursor: pointer;
}
div.content div.gallery_1 {
width: 800px;
height: 135px;
overflow: hidden;
float: left;
margin: auto;
}
div.content div.gallery_1 div.photos {
height: 135px;
width: auto;
position: relative;
left: 0px;
}
div.content div.gallery_1 div.photos div {
float: left;
width: auto;
height: 135px;
margin-right: 5px;
margin-left: 5px;
}