The Summon Cover Image Resolver is a URL resolver that takes a well known URL format and returns the best cover image based on per-client preferences and subscriptions. The cover image URLs are meant to be used in standard HTML <img> tags, and the resolver uses standard redirects and content types to allow browsers to retrieve the images directly. The Cover Image Resolver is not an authenticated service, but the services that a client subscribes to will determine the images that client can access. The response format may be either
image/png. The Cover Image Resolver does not produce images itself, but it aggregates images from several different image providers, depending on user preferences and subscriptions. The quality, size and format of images returned may vary depending on the services a particular client subscribes to.
The URL for the Cover Image Resolver is http://api.summon.serialssolutions.com/2.0.0/image/isbn/<client_key>/<isbn1>_<isbn2>/<size> where <client_key> is a valid Serials Solutions client key, <isbn1> and <isbn2> are valid isbns and <size> is either '
medium' or '
large'. The Cover Image Resolver will return the best available image chosen from the image services to which the client, identified by the given client key, subscribes.
An image URL for a given Summon document in a Search API response can be retrieved from the
thumbnail_l fields. These fields return the small, medium, and large thumbnails respectively. Not all documents have image URLs.
To make efficient use of browser side image caching the Cover Image Resolver uses HTTP redirects. If an image is requested using its well known url that contains multiple isbns and a valid image is found for one of the isbns, the response will be an HTTP redirect to the well known url of the single valid isbn. This ensures that individual images will only be cached once, and the cached copy will be used if possible.
In case there is no available image given a set of isbns and client configuration the Cover Image Resolver will return an HTTP redirect to the no-image image. The no-image image is a 1px by 1px transparent gif, so it can be included in the page without an unsightly broken image icon. All no-image images will be redirected to the same URL to make use of caching. In the case of a no-image, the HTTP redirect is temporary instead of permanent.