I don’t know who needs to hear this, but it seems to come up in my life weekly:

1. NASA images are not in the public domain;
2. They are generally free to use for most non-commercial, educational, & informational purposes without permission, but acknowledgement of NASA is needed (which true PD would not require);
3. For commercial use, no endorsement by NASA can be implied;
4. Images featuring people, e.g. astronauts, need explicit permission for commercial use.

https://www.nasa.gov/nasa-brand-center/images-and-media/