Items in the catalogue relating to particular subjects are linked to the page for that subject.
Selecting Subjects from the list of 'Browse by' options on the home page will take you to the list of subjects. Selecting a particular subject will take you to a list of images and documents in the catalogue linked to that subject:
You can get to the same list from an individual catalogue entry relating to that subject by selecting the term under subjects on the right:
Please note that items may not have been linked to relevant subjects, depending on who was doing the cataloguing. It is always worth performing a search for the subject as well to find other entries which may have been missed.