That's Ryan Neil's hand (Bonsai Mirai) posing for a professional photo with a very large root-on-rock planting. Here's his caption: "In the studio today with @hornbecker shooting for the Artisans Cup promotional material" (from 2015). He doesn't say what the tree's are. If you'd like to see the uncropped original, it's here
We’re on a bonsai forest binge these days, so let’s keep going. Though it’s questionable if you’d call these rock plantings forests, they do share the multiple tree and some of the landscape features you’ll find with more conventional bonsai forests
Three robust Shimpaku junipers on a rock. From the Omiya Bonsai Museum
Empire Bonsai's caption says "Buxifolio Bonsai forest, planted on a rock, by Luisa Alfaro." The Buxifolio part is a bit of a mystery. Buxifolia (with an a) is a species name, but without the genus, it could be any number of things. The leaves look tiny, so we'll try Neea buxifolia.
I borrowed this photo from a Bonsai Tonight post on Penjing. As usual, I'm impressed with the choice of material and the quality of photos on Bonsai Tonight and this one is no exception. For more detail, there are several very good closeups just a click away.