Ajouter une image dans du code html

Bonjour,
j'ai un site sous simpleviewer, et j'aimerais ajouter une petite image .png dans le backround

voici comment est constitué mon site sous simpleviewer:

http://pierrelevallois.toile-libre.org/

et j'aimerais y integrer donc une image en .png dans le fond gris,

quels sont les éléments a rajouter dans le code ?

merci

fichier Gallery.xml :

<?xml version="1.0" encoding="UTF-8"?>

<simpleviewergallery
	
	galleryStyle="MODERN"
	title="Claudine Letrésor"
	textColor="FFFFFF"
	frameColor="FFFFFF"
	frameWidth="6"
	thumbPosition="LEFT"
	thumbColumns="3"
	thumbRows="3"
	showOpenButton="TRUE"
	showFullscreenButton="TRUE"	
	maxImageWidth="640"
	maxImageHeight="640"
	useFlickr="false"
	flickrUserName=""
	flickrTags=""
	languageCode="AUTO"
	languageList=""		
	imagePath="images/"
	thumbPath="thumbs/"
	
>

<image imageURL="images/img1.jpg" thumbURL="thumbs/img1.jpg" linkURL="" linkTarget="" >
	<caption>A VENDRE : 45€</caption>	
</image>
<image imageURL="images/img2.jpg" thumbURL="thumbs/img2.jpg" linkURL="" linkTarget="" >
	<caption>1er tableau : VENDU - 2eme tableau : A VENDRE 19€</caption>	
</image>
<image imageURL="images/img3.jpg" thumbURL="thumbs/img3.jpg" linkURL="" linkTarget="" >
	<caption>A VENDRE : 39€</caption>	
</image>
<image imageURL="images/img4.jpg" thumbURL="thumbs/img4.jpg" linkURL="" linkTarget="" >
	<caption>A VENDRE : 39€</caption>	
</image>
<image imageURL="images/img5.jpg" thumbURL="thumbs/img5.jpg" linkURL="" linkTarget="" >
	<caption>1er tableau :A VENDRE 25€ - 2eme tableau : A VENDRE 25€ </caption>	
</image>
<image imageURL="images/img6.jpg" thumbURL="thumbs/img6.jpg" linkURL="" linkTarget="" >
	<caption>A VENDRE : 39€</caption>	
</image>
<image imageURL="images/img7.jpg" thumbURL="thumbs/img7.jpg" linkURL="" linkTarget="" >
	<caption>A VENDRE : 29€</caption>	
</image>
<image imageURL="images/img8.jpg" thumbURL="thumbs/img8.jpg" linkURL="" linkTarget="" >
	<caption>Réservé.</caption>	
</image>
<image imageURL="images/img9.jpg" thumbURL="thumbs/img9.jpg" linkURL="" linkTarget="" >
	<caption>A VENDRE : 45€</caption>	
</image>
<image imageURL="images/img10.jpg" thumbURL="thumbs/img10.jpg" linkURL="" linkTarget="" >
	<caption>A VENDRE : 35€</caption>	
</image>
<image imageURL="images/img11.jpg" thumbURL="thumbs/img11.jpg" linkURL="" linkTarget="" >
	<caption>A VENDRE : 19€</caption>	
</image>
</simpleviewergallery>

fichier simpleviewer.css :

/*html, body {
  overflow: hidden;
}
body {
  margin: 0;
  padding: 0;
  background: #444;
  color: #fff;
  font: 75%/1.5em sans-serif;
}
.simpleviewer h1 {
  font-size: 165%;
  font-weight: normal;
  line-height: 1.5em;
  margin: 0 0 0.6em;
}
.simpleviewer p {
  margin: 0 0 1em;
}*/
.simpleviewer a {
  color: #fff;
}
.simpleviewer img {
  border: none;
}

/*--- layout ---*/
.simpleviewer {
  position: relative;
  top: 0;
  left: 0;
  overflow: hidden;
  color: #fff;
  font: 11px/1.5em sans-serif;
}
.loading {
  background: url(../img/spinner.gif) no-repeat center;
}
#sv-mobile-flash {
  overflow: hidden;
}
/*--- /layout ---*/

/*--- detail ---*/
#sv-photos {
  position: absolute;
  top: 0;
  left: 0;
}
.sv-photo {
  float: left;
  text-align: center;
  position: relative;
}
.sv-caption {
  background: url(../img/caption-bg.png);
  width: 100%;
  padding: 10px 0 35px;
  position: absolute;
  left: 0;
  bottom: 0;
  text-align: left;
  z-index: 9;
}
.sv-caption div {
  padding: 0 10px;
}
.sv-caption .sv-paging {
  float: right;
  margin: 0 0 0 15px;
  padding: 0 10px 0 0;
  line-height: normal;
}
.sv-caption .sv-title {
  font-size: 150%;
  line-height: normal;
  margin: 0;
}






#sv-prev-photo {
  display: block;
  width: 50%;
  height: 680px;
  position: absolute;
  left: 0;
  top: 0;
  display: none;
  cursor: pointer;
  background: url(../img/empty-pixel.png);
  z-index: 8;
}
#sv-prev-photo span {
  display: block;
  width: 27px;
  height: 27px;
  position: absolute;
  left: 15px;
  top: 50%;
  margin-top: -23px;
  background: url(../img/assets.png) no-repeat -9px -12px;
  display: none;
}
#sv-next-photo {
  display: block;
  width: 50%;
  height: 680px;
  position: absolute;
  right: 0;
  top: 0;
  display: none;
  cursor: pointer;
  background: url(../img/empty-pixel.png);
  z-index: 8;
}
#sv-next-photo span {
  display: block;
  width: 27px;
  height: 27px;
  position: absolute;
  right: 15px;
  top: 50%;
  margin-top: -23px;
  background: url(../img/assets.png) no-repeat -59px -12px;
  display: none;
}

#sv-topmenu {
  height: 38px;
  position: absolute;
  top: 10px;
  right: 10px;
  display: none;
  z-index: 9;
}
#sv-topmenu a {
  display: block;
  float: right;
  height: 38px;
  width: 37px;
  background: url(../img/assets.png) no-repeat;
  position: relative;
  cursor: pointer;
}
#sv-topmenu #sv-open-window {
  display: none;
  background-position: -147px -5px;
}
#sv-topmenu #sv-go-fullscreen {
  display: none;
  background-position: -97px -5px;
}
#sv-topmenu a span {
  display: none;
}
#sv-topmenu-right, #sv-topmenu-left, #sv-topmenu-links {
  float: right;
  height: 38px;
  overflow: hidden;
  margin: 0;
  position: relative;
}
#sv-topmenu-right {
  width: 5px;
  background: url(../img/assets.png) no-repeat -148px -56px;
}
#sv-topmenu-left {
  width: 5px;
  background: url(../img/assets.png) no-repeat 0 -56px;
}
#sv-topmenu-links {
  background: url(../img/assets.png) no-repeat -10px -56px;
}
/*--- /detail ---*/

/*--- error ---*/
#sv-error {
  color: #fff;
  font-size: 12px;
  font-weight: bold;
  line-height: 1.5em;
  text-align: center;
  font-family: sans-serif;
  position: absolute;
}
#sv-error #sv-error-text {
  float: left;
  padding: 0.7em 20px;
  position: relative;
  z-index: 10;
}
#sv-error #sv-error-bg {
  position: absolute;
  left: 0;
  top: 0;
  width: 100%;
  background: #000;
  border: 1px solid #000;
  border-radius: 5px;
  -moz-border-radius: 5px;
  -webkit-border-radius: 5px;
  opacity: 0.5;
  filter: alpha(opacity=50);
  z-index: 9;
}
/*--- /error ---*/


.clearfix:after {
	content: ".";
	display: block;
	height: 0;
	clear: both;
	visibility: hidden;
}
.clearfix {
	display: inline-block;
}
* html .clearfix {
	height: 1%;
}
.clearfix {
	display: block;
}