It is hard to tell from a picture alone. This is because body language does not always tell the whole story. There is also verbal communication. You know, growling, whining, and screeching. The point that this picture makes is that you must take into account what has happened before this picture was taken to fully understand what each wolf is thinking.
Lets take a look at some different types of body language.
First, we will start with tail positions. The picture below just shows half of the story. The other half relates to movement of the tail in the position it is in. We are just going to explore tail positions and leave movements for another time. The tail is held erect and high.