If you're using Buttondown's writing interface in WYSIWYG mode, you can now add custom HTML classes and ALT text to your images without having to drop down to HTML.

Click on the image once you've uploaded it and a little "edit" button should appear in the bottom-left corner!

(Over time, this will also allow you to thumbnail the image, add alignments and captions, and more. But, you know, baby steps.)