You can load your images from Flickr directly into Slideshow CK.
Get your Flickr API
Go on Flickr to login into your account and ask for your API Key. This is needed to load the images.
Get your album ID
Into your Flickr account, you can navigate through your albums and get the url of it. Example with an album url from the account :
https://www.flickr.com/photos/135592606@N05/albums/72157657248195018
The Photoset ID is 72157657248195018 and this is the value that you must set in the field to load the images from this album into your slideshow.
Note that your album must be public for this to work.