[Phanx]

Your first macro actually fails because GetMouseFocus() does not return ActionButton1Icon. It returns ActionButton1.

GetMouseFocus() only returns the top-most mouse-enabled frame. It doesn't return non-frame UI objects (like textures or font strings). It doesn't return frames that aren't mouse-enabled. And it only returns the mouse-enabled frame with the highest frame level/strata.

Since ActionButton1Icon is a texture, not a frame, you won't get a pointer to it from GetMouseFocus().

However, Seerah's solution won't work for your particular case, because ActionButton1Icon is a child of what GetMouseFocus() does return (ActionButton1), not its backdrop. There isn't really a generic solution that will work to get all visible textures. If you're only interested in action button icon textures, the following would work:

/print _G[GetMouseFocus():GetName() .. "Icon"]:GetTexture()

Breaking that down:

1. GetMouseFocus() returns the frame object.
2. :GetName() returns the name of the object it's called on; in this case, the frame object.
3. The string concatenation operator (..) appends "Icon" onto the end of the name.
4. The table lookup in _G returns the object whose name in the global namespace matches the provided table key; in this case, a string consisting of the button's name with "Icon" on the end, which points to the texture object that serve's the button's icon.
5. :GetTexture() returns the texture of the object it's called on.

Note that using this macro on objects that don't have a name will cause an error. Using it on objects that do have a name, but don't have a corresponding "nameIcon" object, will also cause an error.