If you’ve ever rifled through a box of old family photos and wondered who on earth someone was and what their photo is doing in your collection, Jayne Shrimpton should be your first port of call.

The Brighton-based historian and self-styled “photo detective” spends her days recovering forgotten stories and vanished people, and is much in demand for her skills, which allow her to date and analyse almost any figurative image.

A history graduate, she went on to take a two-year master’s degree in dress history at the prestigious Courtauld Institute of Art, before joining London’s National Portrait Gallery as an archivist, where she worked for seven years cataloguing photographs and paintings. It proved the perfect grounding for her subsequent career, which has dovetailed with the burgeoning popularity of family history research and includes work as a columnist for Family Tree magazine and a researcher for BBC One’s Who Do You Think You Are?

The bulk of her clients are people trying to piece together the jigsaw of their heritage and photographs often hold key clues. Just by studying the cut of a subject’s sleeve or the way their hair is styled, Shrimpton is usually able to date a photograph to within a four-year range. By cross-referencing the information with other documents and records, clients are able to confirm someone is who they suspected or, in other cases, are forced to go back and re-examine a whole chapter of their research.

Everything from the studio where the photo was taken to the style and method of photography can provide clues as to the period, while the way someone is dressed or their pose often gives away the occasion – and there is usually an occasion. In the past people didn’t tend to take photographs in the casual, spontaneous way we do today – it was far too expensive and few people would have owned a camera. Most of the images sent to Shrimpton for analysis will have been taken in a professional studio usually to mark a birthday, departure, or even a death.

Her job is working out what and when. While a wedding is obvious enough, it sometimes takes close examination to spot a photo taken to commemorate an engagement. “The clues are that it’s a close-up and the subject’s hand will usually be draped over a chair or somewhere equally prominent to show off the ring.”

Sometimes her work involves looking at who isn’t in the image rather than who is, to identify it as a mourning photograph.

At the table in her home in Chester Terrace, Shrimpton shows me a photograph of a teenage girl she bought in Step Back In Time in Queen’s Road, Brighton, that she believes was taken in the late 1880s (pictured right). The girl is wearing a tall hat, fashionable in that period, and a bustle. Shrimpton thinks the photograph would have been taken to mark the girl’s “coming of age”. This was a formal transition at around 15 or 16 years old when a child was considered to have become an adult and would adopt full adult dress.

“Knowing she is around 15 or 16 then allows you to work out when she would have been born, which can sometimes be the missing information a client needs to confirm an identity.”

In Shrimpton’s latest book, Tracing Your Ancestors Through Family Photographs, she advises anyone trying to date or identify a photograph to look very closely at the image – and not just at the subject. Even a glimpse of background furniture can give a clue as to the period and backdrops often mirror the vogues of the time. For example, a photo of a little boy posed on fake rocks against a backcloth painted to look like the sea reflects the growing popularity of seaside resorts in the 1880s and the rise in photographers working in them.

Other elements involved in identifying and dating photographs are less tangible. It’s important, for example, to consider someone’s social standing and age when attempting to date their clothes – would they have worn the very latest trends or were they likely to have been wearing these clothes for a few years?

Some identification requires good aesthetic judgment in comparing the features in a photograph of a young woman with an older one to work out if they are the same person.

“Judging facial resemblance is a highly subjective issue,” writes Shrimpton. “As humans we all have a natural ability to recognise and distinguish between different faces but levels of observation vary from person to person.”

Then, of course, there are the red herrings. In one of her first jobs as a “photo detective” she was asked to analyse what looked to her like a mourning photograph. “But I couldn’t work out who they were in mourning for. There was an elderly woman in the photo who looked very much like a widow but she was standing next to an elderly man.

“It puzzled me for ages and I couldn’t work out what was going on. After some discussion with the client, it turned out they had added in a picture of the man who everyone was mourning at a later date – which explained why the old man looked a bit like a cardboard cut-out. I don’t think the relatives realised it was a mourning photo. I think they just thought it was a nice family picture and what a shame great-granddad was missing.”

Her work has given her a keen appreciation of proper documentation of family photographs – and the earlier it’s started the better. “The sad thing is that most people don’t tend to get round to doing their family history until they’re retired and by that stage you’ve usually lost the generations who could have given you the information you need.

“People don’t always keep photos in albums and they can end up getting lost in house clearances. When photographs turn up in shops such as Snooper’s Paradise they’re often a long way from the homes or towns they came from and it can be very hard to pinpoint their origins.”

There are many stories destined to remain lost. Shrimpton picks up a postcard photo of a young woman which – unusually – has been signed and dated (pictured far left). The woman is dressed in her Sunday best in what Shrimpton considers to be an average high-street photography studio. The message on the back reads: “For brother Jack, taken July 5, 1912, aged 38. How’s that? Quite young looking! From Kate. PS. Write to me!”

“Every time I look at it, I can’t help wondering who Jack was and why his sister was sending the postcard. Had it been a long time since they’d seen each other? Why? And the message ‘Write to me!’ – it breaks your heart.

“But that’s what keeps my work interesting. You’re always wondering, who are these people? How did they live? And we don’t always have the answers.”

Tracing Your Ancestors Through Family Photographs is published by Pen And Sword, priced £14.99. For more information about Jayne Shrimpton, including upcoming events, visit www.jayneshrimpton.co.uk