Hi JeanieB,
Thanks for contributing to our forum. As Ed suggested, any header and gallery images that are specified for listings you post through Auctiva are submitted to eBay's picture hosting service so you should not have to do anything differently to meet the "at least one eBay hosted picture" requirement that is mentioned in that announcement.
However, it definitely sounds like this upcoming change to eBay's mobile website and/or app *may* cause images embedded within the description of your listings not to show up on mobile devices so potential buyers who view your items on mobile devices may not see the images that normally show up within the Auctiva templates in your listings.
In order to ensure those who view your items on mobile devices can see all of your product images, it may be a good idea to start adding your images to the Optional eBay Gallery Images section on the lister page as well when creating your listings through Auctiva.
All of the images that are entered in the Optional eBay Gallery Images section are submitted to eBay's picture hosting service so doing so should ensure that all of those images can be viewed through mobile devices once this change is implemented.
I hope this helps.
-Mike