Has the portrait ever been quite what it seems?
In most cases, probably not. The dazzling realism of, say, a Titian or Holbein may lead us to assume we're viewing almost a mirror image, but artists have always flattered fee-paying subjects as readily as today's art editors digitally enhance celebrity pics. And pleasing the client is not just cosmetic: an established lexicon of symbolism imbues classic portraiture with coded commentary on a sitter's status, virtues and worthiest attributes.
Modern movements - Cubism, Fauvism, Expressionism - attempted to leap beyond the purely mimetic, with their effect on portraiture prioritising the presence, aura or psychology of an individual.
Photography, briefly, gave us the most accurate documentation of everyday reality, but that, too, quickly became as much about artifice as objectivity - although belief in its authenticity lingers stubbornly to this day.
Contemporary portraiture, however, has many further tricks up its sleeve. Much of today's most exciting use of the genre crams a multitude of possibilities into an action-packed, snare-filled space. Works that are no longer simply depictions of individuals, but portraits, in a more complete sense than ever before, of our own lives and times.
During her long career the artist has consistently appeared in her own photographs, yet always assuming an identity other than her own.
In her first important series, Complete Untitled Film Stills, Sherman posed as actresses from varying movie genres, the production of the images carefully styled to give the requisite sense of authenticity.
Since then, Sherman has adopted many other guises, including historical figures, clowns and even centerfolds. In some of her most recent work, new photo-editing techniques seamlessly duplicate her image so that she appears twice - as different people - in the same photograph.
Sherman's practice challenges our long-held belief in the objective reality of the photograph.
'The camera never lies', yet her self-portraits of people she isn't vacillate between fact and fiction and in so doing, explore further assumptions that many tend to regard as truths. For example, Sherman has often adopted specific gestures, costume or props in order to convey recognisable 'types', a reflection of the societal clichés commonly used to (mis-)interpret those around us.
Japanese photographer Miwa Yanagi likewise plays with the idea of portrait / self-portrait in her ongoing series My Grandmothers.
The artist's work has generally centred on an investigation of women's roles in her native country, and to create the Grandmothers series, the artist interviews young women about the dreams and aspirations they harbour for themselves - however improbable - fifty years into the future.
Based on these comments, Yanagi photographs the women experiencing the scenarios described, yet made up to resemble the old women they will eventually become.
In this way, the photos act as a kind of 'future portrait', investigating notions of time, identity and personal fantasy.
Another Japanese artist, Yasumasa Morimura, has specialised in 'appropriations' of artworks since 1985.
Inserting his own face and body into reproductions of famous works by artists such as Manet, Frida Kahlo or Valezquez, the artist literally stamps his own personality on classic art. He has similarly posed as iconic movie stars, sometimes in elaborate sets recreating stills from films in which they have appeared.
While many see Morimura's flamboyant, camp aesthetic as fun but artistically flimsy, others consider his work more complex.
For example, the images appear to operate as a kind of wish-fulfilment motivated by the artist's fascination with various aspects of fame. By 'becoming' a classic image or celebrity, Morimura assumes some of their instantly recognisable, enduring status.
This approach, as we shall see, is characteristic of several other contemporary portrait makers, and Morimura's obvious appropriation of both high and popular culture certainly provides a clear-cut example of the eclectic borrowings of postmodernism at work. (It's worth noting that the artist has also recreated pieces by Sherman - in which, of course, he poses as Sherman posing, in turn, as one of her own fictional characters).