Hi,

Can you please tell me what is the pop-up for the gallery displaying flickr images (demo.joomlaworks.net/simple-image-gallery-pro)? Is it flickr only?

Thanks.

This is Simple Image Gallery PRO plugin!
Are you referring to the second gallery? (with joomlaDay photos)
If so, this is colorbox pop up engine.
However, there is no pop up just for flickr, you may use them for all your galleries.