Balclutha Museum curator Dr Roz McKechnie said she and her team were not able to pinpoint the date on which a box of about 75 photos was stolen from the museum, although it was likely last month.
She hoped publicity for the theft might help eagle-eyed members of the public spot the photos, if their taker or takers tried to sell or otherwise use them.
"We’re custodians for many of the items at the museum, which are donated by families for safekeeping.
"Although these photos, which range from about 1860-1970, have been digitised, it’s very disappointing to lose the originals, and mystifying as to why anyone would want to take them."
Dr McKechnie said the images had little intrinsic value, although could perhaps be sold on at markets, or reproduced as vintage ephemera.
"We’ve alerted our networks to keep an eye out at markets, and are monitoring online marketplaces such as Trade Me to see if they pop up somewhere. But really we’d like to see them returned to the collection, which we’d be happy for anyone to do anonymously."
The photos depicted scenes of everyday life and buildings from the earliest days of European settlement in South Otago, she said.
She said the theft was only discovered when she came to look for a particular photo recently.
"There had been an exchange of lids, and evidence of boxes being disturbed, and it became apparent this particular box was missing."
Dr McKechnie said thefts from the museum were relatively infrequent, totalling about half a dozen during her eight years as curator.
In common with all small museums and galleries run largely by volunteers, Balclutha Museum relied on good will.
"We’re all devastated any time there’s a loss from the museum. Unfortunately, we don’t have funds for a big security system, so you just have to rely on people’s honesty. Otherwise no-one would get to enjoy this amazing record of local history."
People with information could contact the museum on (03) 418-2382, or online.