Babies may be insatiably photogenic, but somehow they don't really suit the whole business of photography. The flash makes them startle. They wriggle. They cry. They blink. You prop them up with cushions – and seconds later, they're upside down gnawing their own toes. They make Dr Evil hand-signals. They fall asleep. They drool.

And if it's bad now, it was worse then. Now we have cameraphones to record every last gurgle, but for the Victorians it was much more complicated. A 19th-century parent would have to dress the baby in a starchy gown, transport it and perhaps its siblings to the nearest photographer's (or ambrotypist's) studio as early in the morning as possible, climb several flights of stairs to the skylit attic, arrange the family group against the studio backdrop, get everyone to remain completely still for 30 seconds or so, part with a large chunk of money, and then wait several days for the copies to be finished, before sending them round to family and friends as calling cards, or pasting them into albums.

The main problem was the length of the exposure. However bright the photographer's studio, it took up to half a minute for an image to register on wet collodion. Getting an adult to sit completely still for half a minute is a challenge, but getting a wakeful baby to do so is near-impossible. The photographer could position anyone old enough to sit on a chair by placing an electric chair-style head clamp behind them, but the only way of photographing a baby was for the mother to hold it (or dope it with enough laudanum to keep a grown man rigid for a week).

The results were often extraordinary – as a new collection of these photographs, called The Hidden Mother, shows. Though there are plenty of Victorian studio portraits of family groups, there are also many in which the mothers are concealed: they're holding babies in place while impersonating chairs, couches or studio backdrops. They wanted a picture of just the baby, and this was the best way to achieve it. Sometimes, the figures are obvious, standing by the side of a chair and waiting to be cropped out later; sometimes, they really do appear as a pair of curtains or as disembodied hands. To a 21st-century viewer, the images look bizarre – all these unsmiling children strangled by smocking and framed by what appears to be a black-draped Grim Reaper, or by an endless succession of figures in carpets and chintz burqas.

The images in Linda Fregni Nagler's book are touching and slightly macabre. One series has the mothers uncovered, but their faces have been erased to leave nothing but a blackened gap. In others the babies they hold appear to be dead: a couple of smaller photographs show infants with sunken eyes. Until the 1880s and the advent of mass-market photography, most people might only have a snapshot taken once in a lifetime. Since many children did die in infancy, the only memento the parents might have would be the single posthumous photograph of their baby propped up to look as if it was merely asleep.

Hidden Mother

Even if none of the babies in these portraits are dead, there is a creepiness to the images that stems from the photographic process itself. Until gelatin dry plates became available, most photographers used wet collodion. This allowed for much shorter exposure times than calotypes or daguerrotypes – seconds rather than minutes – but the plates had to be exposed and then processed within 15 minutes. Although the resulting images could be well-defined, they made everything look ghostly. Whites aren't white but a sort of looming beige, and the dark draped figures of the women behind makes it seem as if both baby and mother are hovering between one world and the next.

Mark Osterman is a historian who has pioneered the revival in old photographic techniques from his studios in Rochester, New York. "There were plenty of photographers who just specialised in taking babies and old people," he says. "Old people can be shaky and cranky and difficult to deal with, just like babies. So the photographers had to have plenty of light and patience. They might need 18 to 30 seconds to get a clear negative."

Many of those photographers were also female. By the 1860s, photography had become one of the few professions considered respectable for middle-class women: between 1861 and 1871, the numbers of female photographers quadrupled. Just like their male counterparts, they became skilled in keeping babies steady by fair means or foul. Some used animals to pin their attention – keeping pet monkeys or caged birds in their studio – while others resorted to recreational chemistry. One magazine suggested that a dose of opium would "effectually prevent the sitters from being conscious of themselves, or of the camera, or of anything else".

The pictures are poignant for all sorts of reasons, but partly because so few show any of the babies smiling. A baby's smile is too mobile for such long exposures so, as with modern passports, studio photographers demanded that their subjects remain straight-faced, staring out at the viewer with that same expression of impassive wisdom all babies have. It's only when you look past them to these lumpy, human-shaped backdrops that both the babies and their hidden mothers leap out of the past and back into life.