Generate image for rich sharing snippets

I was sharing a SunCalc link when talking to a friend about solar hot water, and it occurred to me it would be cool to generate a snapshot for rich sharing snippets (metadata like OpenGraph images would get picked up I believe).

Crude simulation from Telegram (IM app): http://i.imgur.com/nmTXgNx.png

Maybe this should be optional to save some resources. Say like having a "Generate preview" checkbox under a Share link button?