Open graph can resolve relative url?

Documentation have nothing about it, but relative URLs will not work, only full URL including scheme works.

As long as only full URLs supported you may convert relative to absolute url using URL.Content method (as suggested in What is the equivalent to Page.ResolveUrl in ASP.NET MVC?)

NOTES:

• In 2012 in old Facebook bug tracker this bug was closed stating this is “by design” http://developers.facebook.com/bugs/192471680829756
• If you look into http://ogp.me/ns RDF schema (in Turtle) og:image specified as ogc:url which have next description:

A string of Unicode characters forming a valid URL having the http or https scheme.