Sorry, let me rephrase my previous answer.
There is a built in substitution for the company logo but there are no other image substitutions that are built in.
You’d have to modify the dolibarr source code that does the substitutions, see how it handles the company logo image, copy-paste that, and modify it to do the same thing for the product image(s).
I recently added tags for the shipment module and had to edit a core/class ( core/class/commondocgenerator.class.php) file to make it work - and that file only handles the values, so I could see that it would not be that hard to add a new tag called {product_image} and get the name of the image file from the database, but you’d have to dig into the substitution code ( which is in core/lib/functions.lib.php) to see how to write the image into the odt.
