Visual Arts: A few years back Fergus Martin, previously known for austere abstract paintings and sculptures, took a surprising turn in his work with a set of photographic self-portraits. Not ordinary self-portraits. Our features are not perfectly symmetrical, but with a little technological help, Martin made eerily symmetrical faces by seamlessly marrying two mirror images of one side of his features. The results were both like and unlike him.

In whittling away at the presumed veracity of the photographic image he was also pointing to the way digital technology undermines not just that authority but also - though it may sound a bit melodramatic to say so - assumptions about identity.

Paul Maye's composite portraits, seen recently in Galway, do something similar, offering us entirely plausible individuals who do not, in fact, exist. John Gerrard, whose New Work in New Media is showing at the Gallery of Photography, has plunged into this ocean of possibility with great enthusiasm for the technology and an entirely positive outlook.

Meanwhile, Martin's Green on Red exhibition, My Paradise is Now, is a collaboration with photographer Anthony Hobbs.

It consists of a number of life-size and larger photographs of Martin, digital images of uncanny precision and detail. But where his self-portraits questioned the correspondence of image and identity, here the motivation is to provide a sense of an authentic human presence. There is a theatrical dimension to the exercise.

Martin, barefoot, is garbed in white and adopts contrived poses in a blank, studio-like background. There is something of the outcast about his appearance. He might be a penitent, a prisoner. A huge, composite frieze sees him play the parts of all of the figures in Rosso Fiorentino's Renaissance Assumption. Like Bill Viola, Martin and Hobbs are drawing on the what might be described as the sense of divine immanence in Renaissance religious art, but with something else in mind, appealing to a spiritual element in their evocations of individual human presence in this secularised age.

The show leaves you with the feeling of encountering a real, living person. Gerrard's interactive, three-dimensional portraits, arguably approximating more to an imitation of the real, come across as virtual by comparison.

He is confidently upbeat about the implications of the technology, seeing it as a breakthrough, freeing photography from the frozen moment, the image as object.

He has created a portrait whose eyes literally do follow the viewer, a pair of portraits who respond to each other and to the viewer's actions, a face which will look increasingly sad over the next century. In part, this work can be seen as forming an elegy for his brother who, he notes, died aged only 23. There are also intricately detailed virtual landscapes.

Tellingly, he notes, "virtual landscapes are now challenging real landscapes in terms of their beauty and complexity". The point about real landscapes is that they are real, they are not just eye candy. They are amenable to myriad levels of analysis.

Fabricated landscapes may be instructive in what they can tell us about real landscapes, however they cannot "challenge" them in any but a trivial sense. It could be that we are poised at the edge of an accessible, user- friendly digital technology that will allow for ubiquitous, three-dimensional, interactive photographic images, and that Garrard's predictions will be borne out, but at the moment the issues still look unresolved.

Artists such as Suzy O'Mullane, whose The Weimar Mouth has just finished at the Blue Leaf Gallery, continue to develop work based on one-to-one contact with the subject, in traditional media.

Her drawings and paintings are pointedly informal, even fallible documents, as much records of lived encounters, explorations of appearance and character, as likenesses in the obvious sense of portraiture.

O'Mullane is slow and cautious in the way she tries to figure out what is possible within the confines of the procedure she has adopted.

Perhaps the strongest aspect of her recent show was a series of big, almost architectonic drawings of several subjects.

Their strongly contrasting tonal values and provisional - though very confident - linear armatures made them striking and ambitious images.

There are no images of people in Abigail O'Brien's photographic exhibition, The Rag Tree at the Rubicon Gallery, but the work is nonetheless about the expression of intense human experiences and feelings.

The show's title refers to the traditional practice of tying a rag to a particular hawthorn tree, usually one associated with a holy well.

While there are many complex beliefs associated with the hawthorn, O'Brien has fixed on its role as a kind of prayer tree, imbued with magical, curative properties.

She focuses on one well-known such tree, south of Kilkenny City, and presents us with a series of images of sections of it, thickly decorated with rags in varying stages of decay. There is something poignant in knowing that each knotted rag represents something crucial in the life of the person who places it there.

The effect of the accumulation of these expressions of hope and faith is remarkable, particularly given the sense of time built into the beautifully textured images in the form of progressively more tattered pieces of fabric. O'Brien sees in the practice the persistence of ancient beliefs beneath the veneer of materialistic modernity, which is true enough.

Though it's hardly surprising that people are still superstitious. We are superstitious creatures and probably always will be.

Paradise is Now, Martin & Hobbs, Green on Red Gallery (01-6713414)

New Work in New Media, John Gerrard, Gallery of Photography until November 30th (01-6714654)

The Weimar Mouth, Suzy O'Mullane, Blue Leaf Gallery

The Rag Tree, Abigail O'Brien, Rubicon Gallery until November 22nd (01-6708055)