Yes exactly what @lanthanum says.
There are three themes - broadly 1: family and hobbies; 2: holidays, environment and social issues; and 3: education and work.
Student picks one for the first part of the general convo. Then the photo card is on one of the others; the other one is the rest of the general convo. So yes, all three themes are covered, they don't get to choose a theme that they don't talk about.
But speaking as an MFL specialist this is what I advise: pick the them YOU HATE (so theme 2, usually) for the first part of the general convo. It's your teacher doing it so they could avoid environment or charity (bc let's face it, no one wants those questions) and focus instead on holidays and your town.
Then you get a photo card on education or family/hobbies/celebrations. Happy days.
I have seen students pick hobbies and family as their chosen theme and then get a horrible photocard on charitable donations "what kinds of charities do your friends support and why?" and ofc the teacher cannot change those questions - whereas in the general convo, they can see if you are struggling with a subject and veer away from it.
I conduct a lot of speaking exams for external candidates (HE for example) and I would always pick more familiar areas to discuss - and move on quickly if it was clear the student was strughling (In fact AQA says to do this). But I cannot change the photocard qus and I have seen some tough ones on theme 2.
Apols for essay!