I would probably urge you to not make any opinions based on what you read on the first two links Rigel posted as they are severely out of date. For example, most of them talk about a lack of albums functionality in Xen Media Gallery, and that is no longer true. Xen Media Gallery has had albums now for some time, they were introduced in Xen Media Gallery 2.0 and Xen Media Gallery 2.1 isn't too far away from release now.
I'm not going to steer you towards either, that's going to be an entirely subjective choice you need to make based on what is right for you and your community.
All I would do is ask you to write down what you feel is important in a gallery software, then either ask direct questions about the functionality or trial the gallery for yourself. I'm sure you've seen the demo sites, but just in case:
http://sonnb.com for sonnb XenGallery
and
http://xenmediagallery.com for Xen Media Gallery.
On the subject of embedding Getty Images... In theory it should be simple. Both galleries support the embedding of media in the same way as XenForo handles it in posts. You just provide a URL and as long as you have a BB Code Media Site configured for it, it will embed the content.
In theory it works:
But each embed URL has a unique string at the end. This makes it very user-unfriendly to use. So it may require some custom development - that is regardless of the Gallery solution you use - then that BB Code Media site would be usable in a gallery or posts or anywhere that accepts bb code in XenForo.
Good people to talk to about the possibility of a GettyImages media site are
@JoshyPHP and
@EQnoble.
Good luck in finding the right Gallery for you, I'll be more than happy to ask any questions here, by PM or at
http://xenmediagallery.com.