I did it in photoshop. I think you could do it anywhere really. I made a black box and then changed the pic sizes and copied them into the black box. It took me a while as I never saved the first time round and lost it .
I would liked to have had it so that the tanks (words) were in different colours and then the fish from corresponing tanks have a coloured box round the pic to match but I didn't know how to do the box part.