There is nothing in the General Data Protection Regulation (GDPR) that prohibits people from taking photos in a public place. Provided you are not harassing anyone, taking photographs of people in public is generally allowed and most likely will qualify for the household exemption under Article 2(2)(c) of the GDPR.

However, what you do with that photo can potentially become a data protection issue, for example, if the photograph, which contained the personal data of individuals, was sold for commercial gain or was posted publicly on a social media account. Under those circumstances, you are likely to be considered a data controller which brings with it a host of obligations and duties under data protection law. In particular, it would be necessary for you to demonstrate, amongst other things, your lawful basis for the processing of such personal data under Article 6(1) of the GDPR.