Instead of wading through through yet another page of boring grammar exercise to "help" my students understand the various uses of modal verbs, I decided to use Flickr instead. The basic ideas is that you use the images from the site in order to make guesses about what you can see. For example, use pictures from various parts of the world to practice making deductions about where the photo was taken.
"The picture must be from somewhere cold as all the things are made of ice.
It can't be from Greece as we don't have such shows."
When talking about deductions in the past Flickr provides a wealth of learning possibilities. Choose a dramatic image and ask you student what they think might have happened just before the photo was taken.
"The driver of the car must have been seriously injured.
The lorry driver may have been drunk."