Secretly taken photographs of livestock production systems, representing animal welfare violations, regularly appear in the media and initiate discussions as to the legitimacy of overriding legal regulations in order to document animal welfare standards. This paper focuses on the public perspective and compares different forms of undercover investigation, weighing animal welfare against the invasion of farmers’ privacy. For this purpose, an exploratory online survey was conducted in Germany (n = 292). Participants were carefully selected to ensure that age range, education level and sex reflected the distribution of the society as a whole. In a split-sample survey, each participant was confronted with three scenarios. The scenarios were mapped using pictures showing various levels of farm conditions combined with small information segments describing the invasion of farmers’ privacy. Participants evaluated the scenarios for their perceived legitimacy and whether entering the premises should be punished. All forms of undercover investigation were perceived as legitimate by most respondents. Perceived legitimacy was considerably higher when obvious animal abuse was uncovered. Apart from where damage to property was involved, which was mostly considered as unacceptable, harsher punishment for animal welfare organisations generally obtained little social approval. The public’s increasing awareness of farm animal welfare overruled social norms regarding farmers’ privacy, and thereby demonstrated the importance of animal welfare in society. Approval of undercover investigations indicated that changes in housing and handling conditions as well as improvement in control mechanisms are necessary to increase animal welfare and thus public acceptance of livestock production.