Volusion gives a standard API call with a specific list of fields that may be exported from your store. See this link: Exports: Products Export (Developer)

For photos, they appear to only have pe.PhotoURL_Large, pe.PhotoURL_Small that can be pulled from the Volusion API. This is located under the Advanced Info tab for a product. When you put an image directly under the Image Management tab, it does not populate this image in the Advanced Info tab.

In order to import image URLs, GoDataFeed builds the URL using the productID and static portions of the URL. For example: /v/vspfiles/photos{productID}-2T. From this, we write the URL which we append a .jpg to all photos.  

You will need to either enter the URL values in the correct field on the Volusion product details or create a merge file. Please contact us for more information and assistance.