404error.png
License : Free for commercial use
Source : https://www.iconfinder.com/icons/34268/error_hand_written_icon#size=128

lock.png
License : http://opensource.org/licenses/MIT
Source : https://www.iconfinder.com/icons/1814107/lock_padlock_secure_icon#size=128

search.png
License : http://opensource.org/licenses/MIT
Source : https://www.iconfinder.com/icons/1814075/find_magnifier_magnifying_glass_search_icon#size=256