rm: foo: Operation not permited.

1. List file information.
ls -lo

rw-r–r– 1 fired/staff uchg 1.jpg

2. Remove file 1.jpg from my hard disk.
rm 1.jpg

override rw-r–r- rm/staff for foo ? y
rm: foo: Operation not permited

3. Unlock file 1.jpg with the Terminal
chfags nouchg 1.jpg

4. And now I can remove file 1.jpg from my hard disk.
rm 1.jpg