The Teacher Training Agency advertisement, which carried the the slogan "Use Your Head. Teach", was branded insensitive by some viewers because hostages in Iraq had been decapitated.
Others said the nightmarish images, intended as a parody of people in mundane jobs, were too scary for young viewers.
The Advertising Standards Authority drew attention to the commercial in its annual report. It said 83 complaints were received about the advertisement, making it the 10th most controversial on television in 2004. Communications regulator Ofcom, which handled all broadcasting complaints until November 1 when they became the responsibility of the ASA, decided not to reprimand the TTA.
Ofcom said: "Because the advertisement was on air for some time, viewers would be familiar with the unusual imagery."
A TTA spokeswoman defended the advertisement, saying: "It was incredibly effective. It increased the number of would-be teachers enquiring about a career."
The TTA was also criticised over an advertisement which was aired in late 2004 and early 2005, It showed smiling children along with the slogan "better than any anti-ageing cream". The advertisement was branded unrealistic by teachers and drew nine official complaints. Again no action was taken.
Ofcom, however, upheld complaints against advertisements produced by the Government's Basic Skills Agency, which showed a gremlin taunting a woman about her lack of educational qualifications.
The advertisement which drew 89 complaints, the ninth highest number in 2004, was said to have upset children and Ofcom ordered it to be shown after 7.30pm.
The greatest number of complaints, 1,360, were made about the TV channel Auctionworld. Viewers protested over poor customer service, misleading guide prices and delivery delays. Auctionworld was fined pound;450,000 and had its broadcast licence revoked.