It just strikes me that up till now not even half of the uploaded photographs have a border and title added. It's a pity, too much effort?Anyway, it's a really interesting topic.
Thank you all for your comments and congrats to the winners and of course to those who got it right. These are indeed stackable chairs, it's the 40/4 stackable chair designed by David Rowland, those who are interested can find it on http://www.howe.com/product/404.The shot is taken in Salisbury Cathedral in the UK where old furniture has been replaced by these chairs, see also on http://www.howe.com/sites/default/files/u1/CASE_02_Salisbury_Cathedral.pdf.
Looks like the top of a chess piece.