How to include images when importing blog posts?

Someone can correct me if I’m wrong, but I think if the URLs aren’t changing, or can be fixed with a find/replace of the base URL, then you can copy the images manually to the content folder of your Ghost instance.

I believe Ghost will create smaller sizes of the images on-demand if needed.

If I’m wrong, then yes, using the API or the migration package is the way to go.

You can look for example at the source code of the Jekyll importer, which is another Markdown-based blog solution.