Solution:
 
Delete Border properties in Image tag and Implement below procedure.
 
Place attached file in App_Code
 
 Add below tag in Web.Config

< pages>
< tagMapping>
< add tagType="System.Web.UI.WebControls.ImageButton" 
mappedTagType="BorderlessImageButton" />
< /tagMapping>
< /pages> 

Code:


Add attached file in App_Code Folder

				
using System;
using System.Web.UI.WebControls;

public class BorderlessImageButton : ImageButton
{
    public override Unit BorderWidth
    {
        get
        {
            if (base.BorderWidth.IsEmpty)
            return Unit.Pixel(0);
        else
            return base.BorderWidth;
        }
        set
        {
            base.BorderWidth = value;
        }
    }
}