Hello
You can used simple css with asp button
like
<style>
.button {
border: none;
background: url('Images/Koala.jpg') no-repeat top left;
padding: 2px 8px;
}
</style>
and your code
<asp:Button runat="server" ID="btnExp" Text="Upload" CssClass="button"/>
Please do it if problem persist please give me your comment.