Change those images of image button whos button click in asp

Question

   I have problem I have 10 image buttons on webform1 and when I click on any one button I redirected to the other page with button ID through session or query string. I want to change those images of image buttons whos button click When I come back on webform1.

Protected void Images_Click(object sender, event e)

{

   image img=image(sender);

   Response.Redirect("webform2.aspx?imgId="+img.ID); 

}

I want to chnge image of image button through query string or session when i back on webform1

but how I can determine who button click on webfom1