How to add image numbers in Google Docs

You can use Crossref. The way it works is that you higlight the text referring to a figure, which can be anything e.g. "Figure n" as the add on will replace it.

You then use Ctrl + K to make this into a link to a non existent bookmark such as "#figur_heights" where you can put any text you like after the "#figur_..." Do that for all the figures in the document and when you refer to a figure use an identical non existent bookmark, except it starts as "#fig_..." e.g. "#fig_heights". In this way it can number the figures consecutively and use matching numbers for the in text references.

Finally you then need to go to Add ons > Crossref > Update and it will go through and update all the text for those bookmarks to the sequentially numbered Figure 1, Figure 2 etc. You need to do that whenever you change the order of the figures in your document, add a new reference etc, anything that will change the way the figures are numbered.

so far it is not possible. You could take a look at Google Apps Scripts to create a macro that does that: https://developers.google.com/apps-script/

I've just finished creating a Google Docs Add-on (https://support.google.com/docs/answer/3641454?hl=en) that can number images and tables. It is going through the process of certification by Google and I hope to publish it soon :)

Regards