Display an image on calendar control in a particular date in asp.net using C#

You can use dayRender event of calendar control

 protected void Calendar1_DayRender(object sender, DayRenderEventArgs e)  
 {  
 if (e.Day.Date == DateTime.Today)  
 {  
 Image imageobject= new Image();  
 img.ImageUrl = @"~\images\test1.gif";  
 e.Cell.Controls.Add(img);  
 }  
 }  
This code will show image for the current date.