Before reusing a photograph, connect the permission to the specific file and the way you plan to use it. A broad label such as free does not answer every question about publication.
Check four details
Look for the permitted uses, attribution requirements, modification rules and any restriction on redistribution. Keep a copy of the applicable terms and the creator’s credit with your project notes. A permission record is most useful when it can be traced to the image you actually use.
For public projects, also consider context. Cropping or adding text can change the meaning of an image, and a licence does not by itself make every implied message appropriate.