Why this Parser error

Hi 
 i am getting this parser error frequently,

Parser Error Message: Server tags cannot contain <% ... %>
constructs.
 i used this resolve url in this image tag, if i remove runat="sever" from img tag then it works properly
but i need  to use runat="server" for code behind approach...

<img src="<%=ResolveUrl("~/Rps/images/empty.gif")%>" ID="imgEmpty" runat="server" alt="empty" border="0"/>
can anyone help me
Thanks in advance 
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