I want to ask, if you take other people's photos to participate in some photography competitions and use them for public welfare activities, is this an infringement?

If it is not used for commercial purposes, it is not infringement if it does not infringe on the privacy of others.

Article 100 of China's General Principles of Civil Law stipulates that "citizens have the right to portrait and may not use their portraits for profit without their consent." It can be seen that the behavior that constitutes a violation of citizens' portrait rights usually has two elements: first, without their consent; The second is for the benefit.