Ten real historic door knockers shown with verified Wikimedia Commons and museum collection photographs. Photograph credits: 1. File:Lion Head Door Knocker at Cologne Cathedral.jpg; Reda Kerbush; CC BY-SA 4.0; https://creativecommons.org/licenses/by-sa/4.0; https://commons.wikimedia.org/wiki/File:Lion_Head_Door_Knocker_at_Cologne_Cathedral.jpg; 2. File:Door knocker, N'Kob.jpg; Bernard Gagnon; CC BY-SA 3.0; https://creativecommons.org/licenses/by-sa/3.0; https://commons.wikimedia.org/wiki/File:Door_knocker%2C_N%27Kob.jpg; 3. File:Sanctuary Knocker, Durham Cathedral - geograph.org.uk - 2532705.jpg; Paul Harrop; CC BY-SA 2.0; https://creativecommons.org/licenses/by-sa/2.0; https://commons.wikimedia.org/wiki/File:Sanctuary_Knocker%2C_Durham_Cathedral_-_geograph.org.uk_-_2532705.jpg; 4. File:Germany Rhineland-Palatinate Trier cathedral door knocker right.jpg; Virtual-Pano; CC BY 4.0; https://creativecommons.org/licenses/by/4.0; https://commons.wikimedia.org/wiki/File:Germany_Rhineland-Palatinate_Trier_cathedral_door_knocker_right.jpg; 5. File:Istanbul Turkish and Islamic Museum Cizre mosque doors knocker in 2015 04 9536.jpg; Dosseman; CC BY-SA 4.0; https://creativecommons.org/licenses/by-sa/4.0; https://commons.wikimedia.org/wiki/File:Istanbul_Turkish_and_Islamic_Museum_Cizre_mosque_doors_knocker_in_2015_04_9536.jpg; 6. File:San Jeronimo church Door knocker Granada Andalusia Spain.jpg; Jebulon; CC0; http://creativecommons.org/publicdomain/zero/1.0/deed.en; https://commons.wikimedia.org/wiki/File:San_Jeronimo_church_Door_knocker_Granada_Andalusia_Spain.jpg; 7. File:Roccatagliata Door knocker with Bacchus.jpg; Niccolò Roccatagliata; CC0; http://creativecommons.org/publicdomain/zero/1.0/deed.en; https://commons.wikimedia.org/wiki/File:Roccatagliata_Door_knocker_with_Bacchus.jpg; 8. File:Door knocker, Florence, Italy (16636026240).jpg; Winniepix; CC BY 2.0; https://creativecommons.org/licenses/by/2.0; https://commons.wikimedia.org/wiki/File:Door_knocker%2C_Florence%2C_Italy_%2816636026240%29.jpg; 9. File:Door Knocker Ring MET cdi55-61-34.jpg; This file was donated to Wikimedia Commons as part of a project by the Metropolitan Museum of Art . See the Image and Data Resources Open Access Policy; CC0; http://creativecommons.org/publicdomain/zero/1.0/deed.en; https://commons.wikimedia.org/wiki/File:Door_Knocker_Ring_MET_cdi55-61-34.jpg; 10. File:Ornate Brass Door Knocker.jpg; Rajib.hyderabad; CC BY-SA 4.0; https://creativecommons.org/licenses/by-sa/4.0; https://commons.wikimedia.org/wiki/File:Ornate_Brass_Door_Knocker.jpg;