You can use a single GitHub issue as an image container for a blog post.

The issue can host other images by uploading images as comments. Another approach is to use separate issues to store individual images.

Whatever works best for you, and your organization style.

This five minute video demonstrates how to use GitHub Issues for image hosting. You can use the same approach for cloud-hosting services as embed targets. The video also contains some bonus tips on using the image AsciiDoc syntax.