It's not really something that can be done too easily anymore, and I think eBay would prefer they weren't in listings at all, particularly since active content was banned.
There are alternatives to active content in the guide linked below, and this is basically what they have to say about it:
"Avoid creating your own gallery in a listing
If you create your own in-listing gallery, like the one shown, buyers on mobile devices will not be able to see them. Since more than 50% of shoppers use mobile, that puts you at a disadvantage. Plus, your pages take longer to load with custom gallery images.
While not recommended, you may need to create your own image carousel in your listing by adding HTML and CSS to your item description. Below is one example of how HTML and CSS code can be used to create an image carousel."
Then underneath that is an example of what is acceptable code (scroll down to 'Creating Image galleries' and expand to read:
http://pages.ebay.com/sell/itemdescription/bestpractices.html#ImageGalleryBestPractice
