Structured Data and Blog Posts?

I understand the concept of separation of concerns and I like it. But how does it apply to blog posts in Perch?

A blog post probably has at least a little text and that's a piece of content. Images are other pieces of content, but blog posts may have 0, 1 or many images. Those images may be floated to the left or right, or just be centered. other than putting those images in the "soup of HTML tags," how would Perch manage those a separate pieces of content?

This would be or particular interest if those blog post images needed to be responsive and wished to use picture element/src markup. You could hardly expect the writer to include that markup in their Markdown or Textile text.