The general rule in most countries is that photographing public spaces, streets, buildings, and crowds is legal and normal. Restrictions cluster in predictable places: military installations, border zones, airports and ports in some countries, police operations, and the interiors of certain government buildings. Signs with a crossed-out camera mean exactly what they show, and arguing with security staff never ends well.
Beyond legality, local sensitivity varies a lot. In some countries pointing a camera at strangers is unremarkable; in others it is intrusive, and photographing people, especially women, children, and religious occasions, calls for permission first. Rural and traditional communities are generally more sensitive than big cities.
A few habits keep you out of trouble everywhere: ask before photographing individuals up close, put the camera away when anyone in uniform objects, check drone rules separately since they are strict in many countries, and when in doubt at a sensitive site, ask. Check your destination's rules, as a few countries restrict far more than average.