The answer is HARD
Just like the phrase; a hard nut to crack, the first pictures shows how Hard the nut is to crack.
A stone arrangement which is hard to arrange. Stones are also know to be hard.
The third pictures shows a woman on top of a mountain doing yoga, which is known to be very hard to do on this height
Mountain climbing is known to be a very hard procedure. So this picture also portrays the word hard.
Thank you.