inserting images in varbinary datatype

You should define that column with type Image. Now you can do it like this:

// save image to a memory stream
System.IO.MemoryStream memStream = new System.IO.MemoryStream( );
Image.FromFile( fileName ).Save( memStream, System.Drawing.Imaging.ImageFormat.Bmp );

// create SqlCommand and add a parameter
SqlCommand sqlCmd = new SqlCommand( "INSERT INTO TableName ( ImageColumn ) VALUES ( @Image )", sqlConnection );
sqlCmd.Parameters.Add( "@Image", SqlDbType.Image );

// set image as byte[] to parameter
sqlCmd.Parameters [ "@Image" ].Value = memStream.GetBuffer( );

// execute command
sqlCmd.ExecuteNonQuery( );