Hi,
Thank you for your comment.
Regarding the use with a caching plugin, the issue is mainly with Google Photos, since Google does not give you the actual URL of a photo – it gives you a “short link” that redirects to the actual photo. This short-link has a life-span of around 30 minutes, so when you access it after 30 minutes, the link becomes invalid. That is why it doesn’t make sense to cache it.
For every other provider such as Flickr, SmugMug and Instagram you can cache Photonic’s output (as long as your gallery itself is not changing) – there is no issue there.