Another Optical Illusion: How Many Circles Can You Find?

Here's another optical illusion. It's not as visually striking as the other one I posted recently, but it's interesting (and, unlike the other one, the basic qualitative feature of the illusion is not one that I have not encountered before).

In this image there are 16 circles. Don't you find them? Look again carefully & discover the 'coffer illusion' https://t.co/zPpephKSos pic.twitter.com/fnzOFI83GP

— Massimo (@Rainmaker1973) August 9, 2017