I have a HTML5 website with some pictures and some data about the pictures. I would like to enhance their description so machines would be able to read them as well.
Say, there is a picture of Mona Lisa by Leonardo da Vinci, completed around 1503 - 1519 (n.b. "around" and "range")
What format should I use? What are the best practices in 2012? RDF? RDFa? Microformats? Dublin core? Schema.org?
What is the best way to integrate such metadata into a HTML5 page?
How to express a date which is not very precisely known?