“Repellent” is one word I’ve heard to describe Alastair Adams’ new portrait of Tony Blair, but I don’t know if that’s a reaction to the painting or the subject. In either case, I can’t say I share that gut-reaction. Most of the portraits in the National Portrait Gallery manage to say very little about the subject or their reputation. This one does, so that’s my first positive response to it. 

Face Value – heh, who’d have thought to come up with that title for an exhibition of portraits? Yeah, it’s not particularly clever, but there’s something of the contrarian mischief-maker in it all the same, for in the 50 years that Bob Dylan has been making music, giving interviews and being lionised as the son of God, there’s never been much danger of anyone taking him at face value. Or at least there shouldn’t be. And the same could be said of the 12 portraits that make up this exhibition.

One is increasingly struck by the oddity of an annual portrait prize, or at least I am. Imagine an annual still life award or an open competition for a major prize for abstract art. And imagine how formulaic and stale that would soon become. How many variations of a photorealist table laden with grapes or half drunk glasses of wine could you put up with? Or just think of all those coolly two-tone geometric canvases that’ll come pouring in.

Chuck Close is often described as a photorealist. It’s a fair description. His paintings often look like photographs, and he came to prominence in the late Sixties, when photorealism was the rage. At first his huge heads were scaled-up painted transcriptions of black and white photos, such as Big Self-Portrait, 1968, which is the painting you’ll find in most art history accounts of the period. It captures a kind of rough diamond Easy Rider persona. Then he turned to colour and painted his huge heads as if they were seen through the distorting prism of a bathroom window.

While any Manet survey, however compromised by a lack of significant loans, must be considered "an event", this is not quite the exhibition one might have hoped to see of a great artist. Taking up one vast floor of the Royal Academy with just over 50 paintings (and some not very good pastels), many of which are unfinished and must have been judged unsatisfactory by the artist himself, it is far too thinly spread to be the touted blockbuster it seeks to sell itself as.

The first thing to say about Paul Elmsley’s portrait of the Duchess of Cambridge, which was unveiled yesterday at the National Portrait Gallery, is that it looks rather better in real life than it does in reproduction. That doesn’t make it a great painting, but nor is it a risible one. The soft-focused, Vaseline-smeared visage, framed by that undulating cascade of buoyant hair (it’s unfortunate how much this makes her look as if she's taking part in an ad campaign for shampoo) is more convincingly defined and skilfully modelled than it is when you see it on the screen.

In our chilled Decembers, even when snowless, winter scenes are visually synonymous with Christmas, and Henry Raeburn’s small painting of The Reverend Robert Walker, from the 1790s, skating with abstracted solemnity and perfect balance on Duddingston Loch, only a few minutes away from the National Gallery of Scotland itself, is one of the most irresistibly memorable seasonal images.

Has there ever been a successful portrait of the Queen? Not a photograph - there are been plenty of those (with its delicious air of ambivalence, Thomas Struth’s portrait of the Queen with Prince Philip stiffly occupying two ends of a sofa at Windsor Castle, is among the best) but a painted portrait. Or rather, since we have Warhol’s screen prints which cannot be bettered in the age of incessant reproduction – not to speak of the air of decadent Hollywood glamour she acquired in the process –  an official painted portrait?

The Queen is the first mass-media monarch, and still probably the most ubiquitously depicted person in history. Her 60 years on the throne is only exceeded by Victoria, and her reign has coincided, of course, with photography, film and television. The profusion of royal imagery is exaggerated and exacerbated by the cult of celebrity and the new technology of the internet and social networking. This has led to an overwhelming sense that the public has the right to know the most intimate details of the lives of public figures.