The company appears to be making 600 images at a time available for download.
Just to clarify for the rest of us --
Royalty-free does not mean that the images are free, and it doesn't mean they can be shared.
It means that you buy the image once, it is still a copyrighted image, and you have the ability to use it in your projects without paying a per-use royalty. But it can't be given to anyone else.
I see this a lot on eBay with music samples -- someone will buy a royalty-free sample collection, and then copy it and sell it in quantity on eBay, claiming that because it is royalty-free, they have the right. Not true.