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Article History

Received: 9 January 2025

Accepted: 16 April 2026

First Online: 2 May 2026

Competing interests

: The authors declare no competing interests.

: The study received ethical approval from the University of Sheffield Research Ethics Committee on 03 December 2020 (Ref. 036596). All procedures involving human participants were conducted in accordance with the ethical standards of the committee and complied with the principles of the Declaration of Helsinki and its later amendments. Participation was voluntary and anonymous, and no personally identifiable information was collected. In addition, during the investigation in Chinese cities, the study method also received ethical approval from the School Ethics Committee of Beijing Institute of Technology in 2021 (No. 20210421).

: All image capture and data handling procedures conformed to the approvals granted by the University of Sheffield Research Ethics Committee (Ref. 036596) and the School Ethics Committee of Beijing Institute of Technology (Approval No. 20210421). An opt-out model of informed consent, explicitly endorsed in the approved protocol, was employed because photography occurred in a public space where individual recruitment was impracticable yet participation risk was minimal. Advance information and the right to withdraw were used. Laminated A4 information sheets were displayed at all prominent visible locations of the study area during every observation period. The sheets detailed the research purpose, the potential publication of photographs, and the secure storage of data. Individuals who contacted the research team or indicated on site that they did not wish to be recorded were immediately excluded, and any images already captured were deleted. To date (26 March 2026), no members of the public have contacted the research team or requested exclusion from image recording or data use. To further protect privacy, image anonymisation procedures were applied. All photographs included in the manuscript were cropped and fully anonymised, with faces and other identifying features blurred to ensure that no individual is recognisable. Black bars over the eyes were not used. These procedures satisfied the ethics committee’s requirements for informed consent in public-space research and ensured that all reasonable measures were taken to protect participant anonymity.