You can load the images from a Google Photos album directly in your slideshow. The only thing that you need to do is to give the album url.
Go in your Google account >> Google photos >> Navigate to the desired album >> Copy the page url
You shall get an url like this
https://photos.google.com/share/AF1QipNNAl5oOJRLl0ZNURhzou2UWsGyAJhAfBXDY-Cx2_zROmLEjMtocQrIRCCTEYVMrQ?key=cGc3VkJwWko3el9HSGh3RlcxdkZxYjdYakJNeDBR
Then paste this url into the field in the Slideshow CK module
Note that this will get the image size directly from the album page, there is no option to get a higher resolution. This is usefull if you want to show your album without a very high resolution.