you have the image source set to use the artist picture already:
<img src="uploads/<?php echo $row_rsartistlist['artist_pict']; ?>" name="imageid" width="300" class="rightimmain" id="imageid" />
it is usiong the same image as the mouseover code:
onmouseover="document.getElementById('imageid').src = '<?php echo $row_rsartistlist['artist_pict']; ?>',1)"
the mouse over is just swapping it with the same image