Police are investigating after footage of the incident at The Dickens pub in Cleveleys, Lancashire, reached almost 100,000 views just hours after it was published on Facebook.
The video, now removed on the advice of local police, shows a young man inching towards a Royal British Legion box at the bar, before unhooking the pot on November 3.
The man, dressed in a blue and white sweatshirt, can be seen looking around casually and loosening his trousers, before grabbing the tin and shoving it down.
The pub was notified of the theft after the emptied tin was found in an alleyway by a member of the public who handed it in to the charity.
Pub landlord Brian Jenkinson, 52, said there would have been at least £50 in the pot.
"The box in question was approximately half full, mainly £1 coins as it's the box with all the bigger items in," he told the Press Association.
"We also added £50 from our own charity pot, plus the staff have donated 50% of the tips they have been given to the British Legion poppy box.
"The whole area is outraged at the moment," he added.
Pictures have been posted on the pub's Facebook page in efforts to identify the thief.
A spokeswoman for Lancashire Police said no arrests have been made and an investigation is ongoing.