[Answered ]-Wagtail Image template tags

Currently the rich text editor doesn’t support embedded images with custom attributes (like CSS classes). It also doesn’t provide a HTML source editor for the richtext field.

However, if you don’t need to have the images inline with the rich text (but rather before or after the text, you could include them in your page model using InlinePanel pointing to table which uses a ParentalKey. Then, in your templates, you could loop through multiple images and apply the specialized CSS classes. The Wagtail demo project uses this method to create an image carousel. You can find some explanation on the more general tactic of using ParentalKey/InlinePanel here in the Editing API.