Police said three men called at the home of the 87-year-old woman, in Butterbowl Drive, Farnley, and offered her gardening services.
She paid the fraudsters £400 in cash and they said they would return with a skip until a neighbour confronted them and the trio fled.
It happened between 8.50am and noon on October 13.
And police investigating the fraud have today released an e-fit image of one of the suspects they are trying to trace.
PC Rakesh Rana, from West Yorkshire Police, said: "These men have clearly targeted an elderly and vulnerable victim to take a significant amount of cash from her.
"We we would like to hear from anyone who recognises the man shown in the image or who saw the men in the area."
The other two men involved were described as white, aged 20 to 30-years-old, and slim.
One of the suspects had short, dark hair and was wearing orange workman-style clothing at the time.
Anyone with any information that could assist the investigation is asked to contact PC 504 Rana at Pudsey Police Station via 101, quoting crime number 13160490796.