A new Banksy-style mural is either by "a wannabe" or by someone paying "homage" to the artist, an expert said.
The mural of a boy holding a fishing rod with a blue face mask attached was spotted early on Wednesday, on the sea wall at Stone Pier in Harwich, Essex.
Prof Paul Gough said it lacked the artist's "quality of painting" and careful choice of location.
Tendring District Council has put security in place to protect the artwork.
The work was spotted days after Banksy confirmed he was responsible for 10 artworks spotted across Norfolk and Suffolk, in what he dubbed "A Great British Spraycation".
Prof Gough, vice-chancellor of Arts University Bournemouth, said it was not unusual for similar works to crop up after Banksy had "bombed a part of the UK".
"There are others who will join in, others who try to fake something," he said.
"They want to be a wannabe or they want to pay homage to what Banksy has achieved, so it is probably not a Banksy.
"It's been a massive effort to produce these pieces up and down the East Anglian coast and it's very, very unlikely he and his team would return now."
The artist was an "extraordinary stenciller", with "a quality of painting that is difficult to copy", said Prof Gough, adding that the quality of the Harwich mural did not meet this benchmark.
Banksy also "sites his work extraordinarily well and that's what we're seeing up and down the East Anglian coast".
Again, the professor said the artwork of the boy fishing had not passed this "test".
A genuine Banksy mural in Clacton-on-Sea was painted over in 2014 by Tendring District Council, which has been quick to protect the new unclaimed artwork.
As well as providing a security guard, it has covered the mural with an acrylic sheet.
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