Derbyshire Police realised the CCTV footage following seven robberies in Derby and Ilkeston over the past five weeks.
Police say the suspect has been armed with a knife in each of the incidents to steal significant amounts of money but has not harmed anyone.
Independent charity Crimestoppers is offering a reward of up to £1,000 for information.
Police say the first three robberies happened on October 5 in Derby between 6pm and 9.32pm.
The suspect was described as wearing a bright orange jumper and black trousers.
A shop in Derby was targeted the following day, and on October 14 a shop in Ilkeston was robbed.
Two incidents took place this week in Derby – with the suspect wearing dark clothing with a navy hood.
Chief Inspector Chris Thornhill said: “These offences have understandably caused concern and a team of detectives are following a number of lines of enquiry in an effort to bring the man responsible to justice.
“I know there are people in the community who know who this man is – and they know that the right thing to do is to come forward.
“We have thankfully seen nobody physically hurt in the incidents so far, but any person who is willing to arm themselves with a knife is putting our community at serious risk.
“We are increasing both our uniformed and plain clothes patrols in the city – as well as armed response officers including potential targets as part of their patrol strategies.
“I would urge anyone who has any information, no matter how small it may seem, to come forward as soon as possible.”
Contact Derbyshire Police quoting reference 24000595055 with any information.
To anonymously contact independent charity CrimeStoppers, on 0800 555 111, or by visiting
