You could just link to them I think, possibly with a hint to specify inlining; the client decides whether to obey that hint or to ignore that hint. (This would

You could just link to them I think, possibly with a hint to specify inlining; the client decides whether to obey that hint or to ignore that hint. (This would be done the same whether the picture is part of the document or is a separate file, I should think. It makes many considerations easier to work with.)