This activity is enjoyable and gives a good opportunity for speaking but also can be used to practice various parts of the language such as past simple, 'used to', describing people and modals of deduction.
A week before you want to do this activity, get all the students to bring in photos of when they were a lot younger - if possible, young enough to make identifying that person difficult. The class teacher can also bring in a photo as well as any other members of the staff that the students know well: the secretary, other teachers, the director.
(If the students are studying away from home and can't get hold of photos of themselves when they were young, I have used photos of famous people when they were young. These are easily found on the internet, especially 'biography' sites)
The teacher takes the first photo and elicits language of description such as 'she has a large nose' or 'he has long black hair'.
Information gained from the photo can be used to gain clues about the identity of the person.
- he used to live next to the sea
- she used to have a horse
- he used to have his hair very long
- etc, etc
When it comes to guessing who the person is, this is where the modals of deduction come into play.
- it can't be Johan because he has blond hair
- it must be Carolyn because only her hair is ginger
- it could be Fabio because he lived next to the sea when he was young
- etc, etc.
This part of the game will obviously work best if the students know each other quite well - so you can do a good getting-to-know-you lesson beforehand too.
An interesting follow-up could be getting the students to talk more fully about their childhoods.
A possible variation of this activity: students are given a random photo each for the weekend and have to write a) a description of the picture and b) a prediction as to who it may be and why.