Art that commemorates the dead — that is, the anonymous, multitudinous, generic dead, as opposed to someone you actually knew — is almost always a troubled affair. Consider the last 30 years of public art in Boston intended as an homage to the untimely deceased. The histrionic tribute in Post Office Square dedicated to the Cold War victims of Soviet-dominated Eastern Europe. The misplaced and uncomfortably saccharine Holocaust Memorial behind City Hall. The cartoonish, overblown yet underfelt Irish Famine Memorials at Downtown Crossing and on Cambridge Common; Even the Vendome Fire Memorial on the Commonwealth Avenue Mall with its stage-whisper sentimentality. All point to a systemic shortcoming far greater than the particular demerits of each piece.

The exact nature of that shortcoming is hard to nail down. What I find troubling is the idea of commemorating not greatness but victimization, not the achievements of human beings but their fragility and pathos. And though the art itself isn’t precisely public, the same questions about exploiting human grief for the sake of political favor or artistic notoriety are raised in pointed ways by the often execrable, sometimes luminous show at the Photographic Resource Center that commemorates the six-month anniversary of the September 11 attack on the United States.

The PRC favored a " quiet " opening for the show, in deference to the subject matter. But the work is here, nonetheless. As I moved among the photographs and videos, the installations and mixed-media work by 17 mostly East Coast artists, I found that the egregious work provoked a more ambivalent response than the successful art.

Steve Aishman’s six digital inkjet prints depict various nondescript buildings in and around Boston. The color photos of waterfront condos and triple-deckers are surrounded by hazy, dark, uneven edgings, as if they’d been burned, or as if the photos had been taken using a spy camera. They feel rescued or stolen. But what gives Aishman’s images their contemptible heft is what he’s written by hand under the pictures. On one: " Flagship Wharf/c-12 13th St./Charlestown, MA/Mohammed bin Laden/owns 6 of the condos. " Below another: " Nabul Al Marabh/180 Boston St., 2nd fl/Dorchester, MA/1984-Oct.2000/Apprehended 9/20/2001. "

You could interpret these images as a statement of the dread and danger that now lurks behind the anonymous façade of urban, " civilized " life. But there’s another interpretation. The first image registers as an oblique invitation to recrimination, even violence: if a bin Laden owns property here, we know what to do. The second also intimates vigilante justice, as if an Arab name and the date of apprehension had completed the story.

Robin Masi’s Afghanistan Refugees’ A/dress is quieter but no less exploitive. A flowing, gauze-covered, upright wedding dress whose skirt describes the kind of wide circumference I associate with 18th-century ball gowns momentarily stops you in your tracks. The gown is black. On further inspection, you notice little black-and-white photographic tiles embroidered into vertical pleats on the skirt’s surface. On very close inspection, you see that the images depict Life-magazine-style pictures of refugees.

The insensitivity of Masi’s construction — suffering people rendered as a decorative embellishment — registers as opposite to but no less unsavory than that of Aishman’s. With its academician’s pun for a title, the garment achieves its own kind of cruelty by managing to be funereal and festive at the same time, hinting it might be just the right outfit for dancing on a grave.

An old family friend who taught for years at the Fieldstone School in New York used to tell a joke about the difference between politeness and tact. A man walks into a women’s restroom and, upon realizing his mistake, says to the one occupant, " Excuse me, sir. " Politeness, our friend would explain, is " excuse me; " tact is " sir. "

Tact — in other words, a sensitivity to what’s appropriate in a particular situation — involves generosity of spirit. And another way of understanding the obtuse, often pretentious elements in " 6 Months " is that they’re tactless — with the added dimension that our proximity to the horrors of September 11 renders such tactlessness brutal. Ornit Barkai’s video of a burning candle, called A Moment of Silence, passes off a fatuous cliché as if it were original. Susan Evans’s Little Pieces is made up of strings of lights, like the kind that decorate Christmas trees; they glow inside many picture boxes the size of cigarette packs. The lights lie strewn on the floor, and each of the small boxes illuminates some miniaturized media image related to September 11. It’s cute, disaster made almost frolicsome. No less disappointing and no more inventive is Matthew Nash’s I Watched It on TV, a handmade (for all its slick seamlessness) book with grainy, TV-generated stills of images we all know too well.

The occasional offensiveness and frequent banality of so much of the exhibit makes it especially hard to appreciate the genuine, powerful contributions by Liz Linder of Boston and Martha Cooper of New York. Neither artist indulges in metaphorical constructions (dresses, candles, light boxes); neither does either appropriate ready-made images from the print or broadcast media. And, most telling, neither addresses directly the hideous events of the day. Instead, they take as their subject matter the aftermath of the attacks — namely, the public displays of mourning that sprang up everywhere.

The displays that interest Linder in her God Bless America series are marquees and billboards and advertising signs that have words appended to them — words that become commercial prayers. The results can be hilarious: " Help Wanted/God Bless America, " or " Seafood-Steak/and Chocolate Cake/Prayers for the Victims. " Linder’s ability to find humor — not ridicule but mirth, and not in people’s suffering but on the outermost edges of it — reflects a sympathy and a level of participation sadly absent in so much of this show. " Why Pay More, " begins one of my favorites; the rest of the sign reads: " Bacardi 175 1587/God Bless America. " Linder’s signature sign, " America Will Not Forget, " with the letters of " forget " tilted and askew, packs a devastating degree of tenderness, as if even forgetting could fall apart.

If Linder’s appeal lies in the stark simplicity of her images, the strength of Martha Cooper’s photographs is in their complex but no less wrenching subtlety. Cooper’s imagery maintains a deliberate, even formal distance from the tragedy; she shoots photos of photos. Her contribution comprises nine inkjet color prints, the first of which is entitled Brooklyn Promenade, 9/19. The day is clear, the sun is setting into the postcard-perfect distance of the Manhattan skyline. In the foreground we see tacked to the promenade’s railing a handwritten note with a photo of the same skyline, except only there, in the photo of the photo, do the Twin Towers stand. The note reads, " I took this picture standing at this spot two years ago in late summer. The city looked so strong that day. It still does. "

For me the hardest-hitting single image in " 6 Months " is Cooper’s Bus Shelter, Midtown 9/14, which depicts some of the missing-persons posters that tiled Lower Manhattan buildings for months after the 11th. Bus Shelter centers on two posters. One depicts the face of a man who appears to be in his 30s; above his head are the words " Missing from World Trade Center. " Below his head appear his height and weight, his work address, and a number ( " please call . . .  " ). The other poster has the picture of a young father on a lawn with a toddler; below are the words " Have You Seen My Daddy? "

The greatness of Liz Linder’s art, and Martha Cooper’s, lies in part in their acknowledgment of their limits; they never put themselves in anyone’s place but their own. Would that their humility had informed more of this show.