How to create a button with image and text

Currently I have button on a form and I need to make buttons image but maintain the click event functions that they have. For instance I have a button that says Update. Is there a way to add an image and put text in that image that says Update and maintain it's functionality. here is the code for the button:
<asp:Button ID="btnUpdate" runat="server" Text="Update" Visible="False" />
 
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