“Oh my god, this is Bob Dylan’s art!”

That was the soundtrack at London’s National Portrait Gallery as tourists stumbled upon Bob Dylan: Face Value, an exhibition of 12 pastel portraits painted by the great singer.

Hardcore Dylanologists were nowhere to be seen on the morning of the show’s opening—and for the rest, the realization of what they were looking at dawned slowly. In fact, it was something of a stealth exhibition—no posters announced it, no arrows pointed the way. The museum wasn’t pushing it, perhaps because of Dylan’s bumpy record on the arts circuit. It’s hard to forget the questions of attribution that arose two years ago at his exhibition, The Asia Series, at the Gagosian Gallery on New York’s Upper East Side: paintings he claimed were first-hand depictions of people and scenes from his travels that turned out to be copies of well-known photographs.

Though the title of Face Value is teasingly ambiguous—are we being asked to rate the value of the faces, or are these 12 faces a jury of our peers, judging us?—this exhibition is controversy-proof. The portraits are pre-advertised as amalgamations; part-observed, part-imagined, they conflate the features of real-life sitters, photographic images, and fictitious faces found only in the musician’s fertile brain.

We all know that Dylan can summon up a distinct individual just using words. He never describes the heroine of “Just Like a Woman,” but we know exactly what she’s like. The question is, are his visual portraits as telling as his verbal ones?

It’s hard not to ask the question: If these pastels weren’t by Dylan, would they be here at all?

There’s something unavoidably same-y about the dozen faces on view at the National Portrait Gallery. Each one is given a name and furnished with a title including the word “face,” as in Face the Music: Ray Bridges and Face Facts: Ivan Steinbeck. Art historian John Elderfield writes in an essay in the exhibition catalogue that Dylan meant for them to be “conventional people,” but the unrelenting family resemblance makes them seem anything but. There’s less variety in the faces on the wall than in those of the people looking at them: All the portraits are front-facing, all the noses adaptations of the same elongated triangle. Twelve pairs of identical eyes squint back at you; every neck is thickly set and squat (poor “Nina Felix” barely has a neck at all). None of the three women are particularly feminine: take away the girly collar from “Ursula Belle,” cut her hair, and she could easily be mistaken for one of the guys.

The lack of variety is either down to obsession or it’s saying something. Perhaps it’s Dylan’s way of claiming authorship in the absence of a signature—each face bears a certain resemblance to the portrait he used as the cover art of his 1970 album, Self Portrait.

He refers to the portraits as “character sketches.” The portrait of Ken Garland bears an uncanny resemblance to a Picasso; Sylvia Renard’s razor sharp cheekbones have a hint of Bowie about them; Ivan Steinbeck, with his moustache and British stiff-upper-lip, is reminiscent of John Clease.

Face the Consequences: Red Flanagan is so shaded that the sitter appears battered and bruised; it almost looks like a mug shot: There’s something haunting about each and every one of them. The portraits are hung at face height, yet they’re bigger than life-size, and in a well-lit room, painted only in grey and white, there are no distractions to save you from confronting each head on, staring back at you, holding your gaze. They all look wary; none of them are warm and fuzzy. The closest we come to a smile is Scott Wagner, and even the curl of his lips doesn’t really succeed in making him look any less downbeat.

The blurriness doesn’t help: There’s a sense that the air is a bit thick between us and them. Dylan has gone for a stroke-and-smudge technique, blurring his pastels to create an atmospheric, out-of-focus, effect. Does this make the portraits more suggestive, or simply mark the limits of his artistic prowess?

The National Portrait Gallery is home to masterpieces of the genre, but even comparison with nearer neighbors puts Dylan at a disadvantage. With a saccharine portrait of Kate Middleton 20 yards down the hall, and the BP Portraiture Award Galleries only a couple of rooms away, it’s hard not to ask the question: If these pastels weren’t by Dylan, would they be here at all?

Dylan’s portraits are rudimentary in terms of precision—there’s little if any drawing involved—but that’s the point. His faces have what Elderfield refers to as a “first-take-like quality.” They’re frank and subdued, swift and muffled rather than studied and painstakingly perfected. And it’s easy to see that Dylan is having fun, making good use of his talent. So if you’re wondering whether Face Value is worth a visit, just sing along with one of his best tunes: “Don’t think twice, it’s alright.”

Bob Dylan: Face Value will be on show at the National Portrait Gallery, London, August 24, 2013—January 5, 2014.