how to load image in ImageButton in codebehind?

Instead of using a Literal control, add a panel control and include the ImageButton control in your panel. You should add the controls in the Page Init event

protected void Page_Init(object sender, EventArgs e)
{
    ImageButton imgBtn = new ImageButton();
    imgBtn.ID = "img_id";
    imgBtn.ImageUrl = "~/images/Workflow/digital-signature-pic.jpg";
    imgBtn.AlternateText= "Signature";
    imgBtn.Click += (source, args) =>
    {
        // do something
    };
    Panel1.Controls.Add(imgBtn);
}

You need to add it to a container on the page, see this article:

http://msdn.microsoft.com/en-us/library/kyt0fzt1.aspx

You can't write a server side control to a literal. You have two options,

• either set the image button directly on the page and change the visibility attribute

• Or Add a placeholder or panel control and dynamically add the image button to it, something like this

          ImageButton btn = new ImageButton(); 
          btn.ImageUrl = "my image url";
  
          btn.Click += btn_Click;
  
          btn.ID = "create an ID";
          etc....
          ph.Controls.Add(btn);