In the introduction Sir Anthony Kenny says, "it is not immediately obvious what kinds of picture provide fit material to adorn a philosophical narrative". It might show pictures of objects and places associated with the philosophers, he thinks, and some illustrations of the texts and "a history of philosophy must contain portraits". By far the largest number of illustrations are just that: full-page b&w reproductions of portraits and marble busts of philosophers through the ages. But that phrase, "material to adorn a philosophical narrative", it sounds as if he thinks these pictures are, at best, a decoration. So this isn't like an illustrated car-manual or medical text, where the pictures help you understand the writing; or a good children's story, where the pictures develop the narrative; or an art book, where the text analyses the pictures. Instead, there is this kind of thing, on p.208: a full-page photo of the old British Museum Reading Room, with the caption that it opened in 1842 and was where Marx worked on Das Kapital.
The drawing of Bentham's Panopticon, mentioned above--it's the grandfather of all prison and hospital design, because one person located at the building's centre can monitor all the prisoners/patients, and it is disturbing because it shows how easy it is to control a large group of people. It is perfect for this book, except that the caption has no explanation of what we are looking at, or how it worked! The writers, Kenny and five others, just don't seem to have their hearts in a graphic presentation. At the back is a 'Chronology' section, where you see what else was happening in the world during the lives of the philosophers. It would have been much easier to read in colour, but you just get two typed b&w lists.
I bought the book because I'm interested in the relation of philosophy to the visual arts (aesthetics, for example). I inferred from the publisher's blurb that I might find this book useful, but in fact I didn't. It is simply part of an OUP series of "Illustrated Histories"--there's one about the Royal Navy, one on New Zealand, one about medieval history, etc.
As others have said, the writing is good at explaining difficult philosophical ideas, and so it is too bad that not as much thinking went into the illustrating. What a shame, it's a missed opportunity. As such, it is still an okay general history, though in my opinion it isn't as helpful as John Cottingham's Western Philosophy, An Anthology (of original texts, with commentary). Cottingham has a chapter on beauty and art--including Kant's Critique of (aesthetic) Judgement, a text that, oddly enough, isn't even mentioned in the Illustrated History, which has a chapter on political philosophy instead.
Kenny may, I think, have a sense of ironic humour. There is one picture of "leading philosophers", taken in 1976 at an Oxford conference: three rows of incredibly nerdy-looking men, and two women.