When you look at that picture, you can obviously only see what a human can see. In fact, photographs and monitors are made for human eyes seeing things as a human would see them. A pig looking at this picture on my monitor might understand the image but think the colors are slightly off.

If a pig saw these three pigs together in person, they might tell them apart for different reasons than you, a human would.

And these are domesticated pigs, bred to look the way that a human wants them to look. Easy for humans to tell different breeds apart.