Note: Since this tool was published, google docs has introduced "Wrap-text" and "Break-text" options for images, which both prevent the add-on to create captions for those images. Unfortunately I haven't yet found a way to insert captions on such images, when I do, I'll make a new version. Until then, the only "style" that's supported is "In line". (Click on an image and you'll see the 3 options on the bottom). I understand that this might be limiting, but there is not much I can do about it.
In addition, google has made it very difficult to publish new add-ons as well as any updates, as you have to go through a lengthy review process, so even this "note" would be tricky, that's why I'm doing it through the "review"... (and if you wonder why I gave my self 5 stars, well, I had to put something, so why not 5 :) )