This is a really basic test of Google ARCore.
I followed the step-by-step instruction from Google ARCore 's Getting Started with Unity
and the only thing I did was replacing Andy's shadow png into my own dog footprint drawing with the original name.
(And I "hide" the Andy obj by replacing a random obj file into Unity, the program seemed failed to load it, so it did not show up in the final app.)
I am not a programmer, I know I am stupid.
But hey, it works!