While there is a very small amount of compression that occurs for some image file types when they are uploaded to an Auctiva account, the actual size of your images should not be affected by loading them to Auctiva.
If you refer to images on listings you created on eBay that have not ended, these would only show on your Active listings page - the images you uploaded to eBay when creating the listings would not be affected by an Auctiva account. eBay hosts the images for the Header and Gallery and for any images you add using eBay directly for your listings, and our system would have no effect on what is already stored on eBay.
As for importing active listings into an Auctiva account, while the process is usually fairly rapid, it can take up to 6 hours for all of your listings to import into your Auctiva account. If you note that there has been a delay of longer than this, please feel free to file a support case from under the Help tab of the site letting us know and we can take a look into that for you.