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Why is the value of GalleryURL returned in the response not the same for different API Calls?
The PictureDetails.GalleryURL returned for a single item may vary, based on the API Call used to retrieve it. It will vary between two different values, as noted below.
GetItem and GetSellerList
The calls above return the actual URL sent in by the Seller of the item for use in the Gallery. The image may either be an eBay EPS hosted image, or may be an image hosted by a 3rd party. For example, the response from GetItem returns a picture details node such as the example below. In the example below, it is clear that the image is hosted via eBay EPS, and that the same image is used as the PictureURL and the GalleryURL.
Search calls such as Finding findItemsAdvanced call
When an item is listed with Gallery, eBay retrieves the Gallery image, and creates a thumbnail version of the image to store locally. The calls above return this version of the Gallery image in the <GalleryURL> output element. At this time, thumbnail images can be recognized as beginning with http://thumbs.ebaystatic.com/pict/* however, this image location could change in the future. For example, the PictureDetails node in the response of these calls may look similar to the example below: