Image On Click

<FORM Action="<%=Request.ServerVariables("SCRIPT_NAME") %>" Method=POST>

<Input Type=Hidden name="CurrentPage" Value="<%=CPage%>" >
<% If CPage 1 Then %>
<Input type=Submit Name="Submit" Value="Previous">
<% End IF%>
<% If CPage <TotPage Then %>
<Input type=Submit Name="Submit" Value="Next">
<% End If %>
</FORM>

this function i want to call when i click an image. i mean i have previous and next image in the page. when i click previous image i want to call this function.