This tutorial shows how to upload images on eBay using different options in Description settings.
Main Image
The Main Image is the image, that appears on the top left of your eBay item and next to your item's title in search results.
To upload this image you can use 2 options:
- Product Base Image – the image marked as a Base Image in Magento will be uploaded.
- Magento Attribute – must be Media Image type or contain absolute url (e.g. http://mymagentostore.com/images/baseimage.jpg).
Default Image Url (optional) – if the main image is not found this image will be used instead.
Fill in this option with absolute url.
Super Size
If you want to see larger and more detailed images on eBay (up to 800w x 800h pixels - 800 pixels on the longest side), use the Picture Pack option. Be aware, it may come with additional fee.
Gallery Images
If you want to upload more than 1 image, use the Gallery Images option. This allows you to add up to 11 additional images that will appear as a small thumbnails under the Base large image.
You can set the Number of images you want to add (the images will be upload from the Magento product images). The images will appear according to the order that you have set in Magento.
Excluded images will be ignored and will not be sent on eBay.
Exception: If you mark Base Image as Excluded, it will appear on eBay anyway
Or specify the images via Magento Attribute.
Only Text, Multiple Select or Dropdown type attributes can be used and must contain absolute urls. 
In the text type attribute urls must be separated with comma.
e.g. http://mymagentostore.com/images/baseimage1.jpg, http://mymagentostore.com/images/baseimage2.jpg
Change Images for Attribute (Only for Configurable products) – changes images for selected option of multi variation items.
To understand better how the settings work for products with variations read the following examples: