Exhibitions: It's a Picassophile's dream

I put all the things I like into my pictures," Picasso stated in 1935. His breathtakingly productive career spanned 70 years, and as the 20th century's greatest assimilator of new ideas, techniques and subjects, he constantly strove to find new subjects to paint. He started taking photographs when he moved to Paris in 1901, aged 20; these, and other images he collected, became source material for his paintings. And now, such photographs form the core of the Barbican's exhibition, curated by Anne Badassari, who claims to have uncovered this last "unknown" area of Picasso's work during her five years of research into the subject at the Musee Picasso in Paris.

The panel introduction that precedes room one boasts that the exhibition introduces "for the first time the hitherto unknown link between photography and Picasso's creative process." But isn't this a case of a bit too much artistic licence? We know that Picasso's patron Gertrude Stein recalled him showing her his photos of the Spanish village Horta de Ebro in 1909, to demonstrate how Cubist the real world was. Alfred H Barr, director of New York's Museum of Modern Art in the 1930s, connected Picasso's paintings to amateur snapshots. We have always known that Picasso collaborated with surrealist photographer Man Ray on "Rayographs" in 1936, and worked with his one-time mistress, Yugoslav photographer Dora Maar, on recording the progress of his 1937 masterpiece, Guernica. But although this show presumes that we are ignorant of these known photographic links, it does present a useful chronological display as evidence of Picasso's continued interest in the photographic process: as documentary tool, painting aid, and artistic medium.

The last five or so rooms - which cover Picasso's neo-classical and surrealist periods, and his later collaborative projects - are more resolved than the first five, and as a result the show starts in a disjointed way. Small photographs the colour of tea, toned from milky Earl Grey to well-brewed Assam, are interspersed with a few of his drawings. The only interesting visual link between these photos (not by Picasso) and his work is a phototypegravure called Fregoli in the role of Paganini, which Picasso studied for his 1905 drawing Portrait of Paganini, the violinist. Picasso's interest lay with the larger-than-life hand that was spread-eagled on the violin's neck. The implicit artifice in the title is also interesting - the name of the Picasso implies that the figure is Paganini; the figure in the photograph is Fregoli. But as Picasso rarely titled anything, we are left guessing who it really is.

Not so with his 1918 portrait of his first wife, the Russian ballerina Olga Khokhlova. The painting and corresponding photographs are doppelgangers, and Picasso said that this painting was "in the style of a photographic enlargement". And yet, the painting in reality owes little to the photograph. Could it be that Picasso took the photo as Olga modelled for the portrait, as a record, in the same way he sometimes took photos of the objects he was painting as still-lifes? The painting owes more to the spatial flatness of Cezanne's Woman with a Coffeepot than to photographic reproduction. Picasso painted her from a higher viewpoint (her left arm is fully visible; her neckline appears lower; he looks down on her face), and her dress and chair appear almost flat.

Picasso used photography as a tool, to document the progress of his paintings and record completed work in his studio. There are rather too many of these photographs in this exhibition - bleached aides-memoire that were intended for private, not public, use. Picasso also collected anonymous photographs, bought cheaply at the flea markets (photography was over 50 years old, and developing fast). Looking at his collection - visiting cards of anonymous city dwellers, ethnographic photographs and postcards (one of which made an interesting comparison with a sketch for Les Demoiselles d'Avignon) - is rather like looking through someone's shoebox of memorabilia kept under the bed, an intrusion into privacy.

Picasso liked to photograph his friends. Fellow Cubist Georges Braque is caught looking remarkably like Picasso, all heavy-lidded sexuality and stocky authority; Guillaume Apollinaire, writer and champion of Picasso, looks very Sherlock Holmes; Daniel-Henry Kahnweiler, the dealer who sold Picasso's Cubist work by the square foot, looks rather fat- cattish, like a post-A levels Billy Bunter. However, two portraits stand out. One is of Angel Fernndez de Soto, the languid young dandy Picasso called "an amusing wastrel", and who Picasso often painted. Picasso's photograph captures his lantern jaw, impoverished-aristocrat look, and pale, staring eyes, all held in place by his immaculate parting of his hair. The other notable photograph is of artist Marie Laurencin - which is interesting less for her chic beauty than for the unfinished 1911 Cubist painting (a portrait?) behind her in Picasso's studio. And it is amazing to see how he painted- the photo shows an almost abstract, hermetic cubist work with the top part of the painting finished. Halfway down, the painting stops, drawing a neat horizontal line across the white canvas, under which only a few cursory pencil strokes can be seen.

Picasso seems least comfortable with a pencil when appearing to copy photographs. His 1916 drawing of the wounded Apollinaire from a photo of the same year is sketchy and uncertain; his "Man with Moustache leaning on a Balustrade" is a clumsy pastiche of photographic material. Yet many of the drawings in this show are fiercely assertive- again this suggests, as does Olga in an armchair, that photography, while an important source, was not the direct inspiration that it is at times heralded to be in this show.

The exhibition as a whole is a Picassophile's dream - archive photographs of every stage of his life and work, his colleagues, lovers, and a film of him painting on glass. It is sad that photographs from outside the Musee Picasso archive have not been included - chronophotographs by Etienne-Jules Marey for example, which must in some way have informed Cubism. But what is included makes it a show to appeal to the Picasso- anorak in all of us. Whether you laugh at his old-man doodles on glossy magazine pages or wonder why he dressed as a soldier for his 1910 self- portrait, you'll feel you've got to know the man behind the myth just that little bit better.

Barbican, EC2 (0171 588 9023), to 28 Mar.