If artists such as Yasumasa Morimura delight in facilitating recognition, UK artist Gillian Wearing partially or completely disguises subjects in order to emphasise alternative aspects of their identity. Masks, in particular, are a favourite form of concealment.
In a 1994 video, members of the public responding to a small-ad invitation to "Confess all" donned party-style rubber masks in order to anonymously reveal misdemeanours, vices and personal traumas.
A year later, Wearing filmed herself walking through a busy London street with her face completely bandaged (above).
Based, as the title suggests, on a real experience, the true subject of this movie portrait is not the artist herself, but the reactions of those around her as well as the unknown woman who inspired the piece.
In later works, Wearing conceals the identity of subjects through far more sophisticated means.
At first, 'Olia' appears to be a sensitive, though fairly conventional photographic study of a naked woman. Yet there is something disquietingly unreal about the figure, and in fact, the image depicts a model 'clothed' in a latex cast of her own face and torso.
In order to understand this portrait in any conventional sense we would literally need to delve beneath the subject's skin, and here, as in Sherman's work, the artist forces us to question the notion that photographic images are indeed authentic and absolute.
In 2003 Wearing again used herself as model for the elaborate project 'Album', in which complex prosthetics transform the artist into members of her immediate family, as well as a teenaged depiction of herself.
Although the disguises - created in collaboration with the famous waxwork museum Madame Tussaud's - are extremely convincing, Wearing takes pains to reveal her strategy by openly terming each work a 'self-portrait'.
Thus asserting her own identity, the portraits become a statement concerning the artist's perception of family ties. Her striking visual conceit claims that, in a very real sense, genetic and social links mean that she is, at least partly, each of the people she portrays.
A further project - and one of the artist's most recent - moves the emphasis away from photography to reflect instead on the artifice of the painted portrait.
The seven slickly erotic Pin Ups have clearly been created according to the conventions of glamour modelling, and could easily represent idealised fantasy figures derived entirely from the imagination.
Yet each portrait (commissioned from illustrator Jim Burns) is of a real subject - two men and five women - who Wearing located through an ad placed online, then sent for a make-over and photo-shoot before passing the images to the painter.
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In a fascinating twist, each of the paintings hinges opens to reveal a hidden archive. In it are the subject's original responses to the ad; a letter explaining his or her reasons for wanting to be represented in this way, and several personal snapshots. Needless to say, these photographs rarely coincide substantially with the subsequent portrait.
While Wearing's project cleverly investigates the chasm between notions of painterly reality and photographic verisimilitude, one of the most powerful statements on this subject lies in Gerhard Richter's celebrated 'photograph-paintings'.
Although the subject matter in these works varies considerably, many are ostensibly depictions of individuals ranging from family members to historical figures or faces simply snipped from magazines or newspapers.
Far from accepting these works as portraits in any conventional sense, however, Richter has always stipulated that they should be seen only as portraits of photographs.
The distinction is subtle yet immensely profound, and in practice, highlights our instinctive need to assimilate and prioritise the human presence above all else.
While Richter's early photo-paintings visually support his contention through black and white imagery and hazy, indistinct brushwork (see image, top of page), later paintings are highly realistic, with a slight blur serving as the only distancing mechanism.
In Richter's painting featuring his baby son, above, our emotional engagement and perception of the image is almost inevitably directed towards the figure of the child - even if we know that the real subject of the painting is not, for Richter, the boy himself, but the photograph in which he is depicted.
Portraits that aren't: continued >