the woman in the first pic suffers from obesity.That's too much meat for me,but anyways
You can't get rid of a big "arse" with certain excercises.Maybe tighten it,but it won't get smaller.The fat will still be covering the nice lean ass.Proper diet and excercise will get rid of fat which in turn will minimize it's size.
See,the body chooses where it wants to store fat.For men,the body likes to store it in the abdomen area.In women,the body likes to store it in the hips and buttocks area until the fat cells become filled up and swollen,then it moves on to store in the arms and abdomen.That's why sometimes women have thin waists and large behinds.
Now when you diet,the last place the body takes off the fat is the ass,so it might take a little hard work.