This plug-in for Micro.blog replaces your Archive page with a new page designed to group your blog posts by year and month. It also has a setting to include a small photo thumbnail preview for any blog posts that include photos.
If you want to control the size of the thumbnails, use a little custom CSS on your blog like this:
.archive_posts img {
height: 100px !important;
width: auto !important;
}
You can set this on the Design page → Open Theme → Custom CSS. If you're using Micro.one, it's under Design → Edit CSS.