In the previous chapter, we built the libcurl library. As a refresher on how to download a web page, refer to the 1_CurlDownloader
example in the accompanying materials for this chapter.
The information about using Picasa and Flickr in C++ is somewhat limited, but calling the REST (Representational State Transfer) APIs of these sites is no different from downloading web pages. All we have to do is form a correct URL for the images list, download an XML file from this URL, and then parse this file to build a list of individual image URLs. Usually, REST APIs require some form of authentication using oAuth, but for the read-only access, it is sufficient to use only the application key, which is available through the simple online registration.