Inserting logo in header, how to?

Hi

Can any one tell me how to insert a logo (jpg file) into my header on my page in upper right corner https://www.mhoey.eu?

If you look in stylesheets, it look like this, I would like to keep the background, and just inserting the picture on the background of the header.

This is the body in the header, found under stylesheets:
body{
background:#f8f8ec url(images/bg.jpg) repeat-x top left;
color:#151515;
font-family: Verdana, Georgia, “Times New Roman”, Times, serif;
font-size:72.5%;
line-height:1.4;
margin:0;
padding:0;
text-align:left;

This is the pictures that normally are shown in upper right corner, designed by the theme designer:

}
#portrait-bg {
position:absolute;
width:319px;
height:221px;
right:0;
top:0;

Or should I look else where?

Hope some one can help me, thanks in advance.

Mick