In this photograph of Tom and Cameron hugging, Ms. Diaz is more affectionate than Mr. Cruise. First notice how Mr. Cruise is turned away from the hug. His feet and his body are pointed away from Cameron. When the lower body is turned and separated in a hug, there's not much affection. He's also only hugging with one arm. It would be interesting to see what his eyes look like, but his mouth is certainly not consistent with happiness. His mid-face and mouth are tightened. Mr. Cruise is normally pretty good at expressing a smile when he tries, but here we glimpse into his actual emotions in real-time.
Cameron leans into the hug, and although her lower body is still separated from Tom she is showing more affection (The most affectionate hugs are when the lower bodies are touching as well as the upper bodies). Ms. Diaz's feet and her entire body are pointed towards Mr. Cruise and she is hugging with both arms. I'd wager she had a true smile on her face at the moment this photograph was taken.