Pictures for an item are uploaded on the "Pictures" tab. However, if your pictures didn't appear or you're having other issues, click the "Force re-send pictures" button on the Hoarde panel on "Marketplaces / portals" tab for an item to force the link to re-send all the pictures from your website over to Hoarde and the images will be re-sent when the link next runs (usually within 10 or so minutes).

Please make sure you've finished uploading your images via the "Pictures" section before pressing this button