Hi,
Accessing Elements inside gridview or repeater directlyis quite difficult, try jQuery instead by its css property
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
<script language="javascript" type="text/javascript">
function fun1() {
$('.MyButton').css("display", "block");
}
function fun2() {
$('.MyButton').css("display", "none");
}
</script>
and add cssclass property to your button like
<img src="<%#"uploaded1/"+ Eval("image") %>" alt="<%# Eval("image") %>" id="profile_pic"
style="margin-left: 4px; width: 180px" height="200" onmouseover="fun1()" onmouseout="fun2()" />
<asp:button id="chng_profilepic" runat="server" text="change profile" onclick="chng_profilepic_Click" cssclass="MyButton" xmlns:asp="#unknown" />