There is an update regarding importing via the automatic generation of URL's because Google does not accept this anymore for security reasons. Therefore you've to deal with other options :
-If the images have already their URL then you can import them easily via a CSV file.
-If the images don't have the URL but have something in their name that refers to the product you want to link it, then you can ask a Tech to do a script import.
-If the images don't have anything of these options above, then you should upload them in Odoo product per product manually.
What I did was using this external website : https://postimages.org/nl/ to generate the URL but still you need to generate the links one by one but at least you can import them all together (again in a CSV file).
But it's up to you to decide what's quicker.