This depends on the source. While there's no copyright per se involved, most people get this sort of data from a source like Ancestry.com, of FamilySearch or Findagrave, and they have limitations as to what can be posted on another website. So,say, for gravestone pictures you didn't take yourself, you need to at least cite where you got it and if you don't have permission from the person who took the picture (in the case of findagrave,) you shouldn't post it on Wikitree. You can link to the picture on a biography, which works well on Findagrave or Familysearch, but not so well with subscription sites like Ancestrry.com. You might want to look at profiles which do have such documents and see how they do it.