Visual material on this site consists of proper materials, as well as others which have been collected over the years from friends and colleagues. Additional materials have been sent to me, but I am unable to confirm their originality and in doing so, I except no responsibility for material which has been copied from another source as these are believed to be public domain. The use of materials here is purely educational and therefore, no reference is made as to the origin of the material.
   Thanks to all who contributed material.