SkeletonAnimation at its core is something that holds and animates Spine skeleton data, and then converts it into a UnityEngine.Mesh for rendering.
So your question may be: "how do I convert a UnityEngine.Mesh into an image?"
This involves rendering the mesh onto a Render Texture. You can check Unity documentation on how to do that. It's sort of specific to how you want your setup to work.
Your question may also be, "how do I render a skeleton in the UI?"
In which case, that's done through the SkeletonGraphic class. When you instantiate your skeleton, instead of choosing "SkeletonAnimation", choose "SkeletonGraphic (UI)".
