I'd like to add sequentially numbered labels to images in posts. Just a small number in the corner of each image to help when referencing them in my writing.
All of the images are wp-block-image (no galleries). The numbering should be simple +1 addition based on the order of appearance in the images for that post (top left = #1, next img = #2...)
The order isn't expected to change after the post is published - it's static content - but in draft stage the images are moved and will be out of order from their upload/inserted/filename/ID.
A few gallery plugins appeared in search that claim to have this feature, but I don't think they'll work with wp-block-images and my existing content. And I'd rather not use a plugin if it can be handled cleaner without it.
How would you add these labels correctly and efficiently?