I checked your code and seems to be no problem at all. please make sure Image commandArgument getting value. check it first binding in label whether you are getting value.
However, here is sample which I'm using in my project
<asp:GridView ID="GridViewUserScraps" ItemStyle-VerticalAlign="Top" AutoGenerateColumns="False" Width="100%" runat="server" OnRowCommand="GridViews_RowCommand" >
<Columns>
<asp:TemplateField SortExpression="SendDate">
<ItemTemplate>
<asp:Button ID="btnPost" CssClass="submitButton" Text="Comment" runat="server" CommandName="Comment" CommandArgument='<%#Eval("ScrapId")+","+ Eval("UserId")%>' />
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
first bind the GridView.
public void GetData()
{
//bind ur GridView
GridViewUserScraps.DataSource = dt;
GridViewUserScraps.DataBind();
}
protected void GridViews_RowCommand(object sender, GridViewCommandEventArgs e)
{
if (e.CommandName == "Comment")
{
string[] commandArgs = e.CommandArgument.ToString().Split(new char[] { ',' });
string scrapid = commandArgs[0];
string uid = commandArgs[1];
}
}