I assume that was just used as an example texture--you could include any PNG file in your project and call it pig.png, no? I'm not sure why the exact image would need to be provided, at a glance it doesn't look like there's any sort of fancy UV mapping happening in the examples.
The first example is a rectangle of dimensions image width x image height, and the second appears to just be a circle. If you wanted the image to be completely unscaled, any ol' 100x100px image will do--but regardless of what your image's actual aspect ratio is the uvs in that one will just stretch it to fit.
It'd be cool to see pig.png, it's probably pretty cute, but I really think you can use any texture with these and get the correct result.
I don't know your skill level, so apologies if the following is just stating the obvious. But just in case anyone looking at this thread doesn't know, UVs are on a scale of 0-1 which maps to the dimension of the texture when sampling on the GPU. You can take any two images, and regardless of their dimensions you'll get the same relative regions from one set of UVs. Thus, when the UVs are just a rectangle covering the whole thing and a circle covering the whole thing there's no difference between what parts of the images will show up.