How to implement mouseover effects in a <asp:image> web server control

<asp:Image id='Image1' runat='server' ImageUrl='b2346.jpg'></asp:Image>

VB.NET

Image1.Attributes.Add('onmouseover', 'this.src=’b2456.jpg’')

C#

Image1.Attributes.Add('onmouseover', 'this.src=’b2456.jpg’');