Two bulldogs in New York City. Original image from Carol M. Highsmith’s America, Library of Congress collection.… https://www.rawpixel.com/image/3092569/free-photo-image-dog-walkers-new-york-cityFree Image from public domain licenseWalker's Universal Mixture, for scour in cattle : a certain and speedy cure : [red label] / B. Walker. https://www.rawpixel.com/image/13961980/image-background-animal-public-domainFree Image from public domain licenseWing chord extension on D-558-2. Original from NASA. Digitally enhanced by rawpixel. https://www.rawpixel.com/image/441383/free-photo-image-plane-airplane-aircraftFree Image from public domain licenseD-558-2 Aircraft on lakebed. Original from NASA. Digitally enhanced by rawpixel. https://www.rawpixel.com/image/441429/free-photo-image-space-aircraft-carrierFree Image from public domain licenseFlorence Nightingale. Photogravure by E. Walker, 1887, after Sir W. Richmond. https://www.rawpixel.com/image/14010104/florence-nightingale-photogravure-walker-1887-after-sir-richmondFree Image from public domain licenseWalker's Universal Mixture, for scour in cattle : a certain and speedy cure : [white label] / B. Walker. https://www.rawpixel.com/image/14021872/image-paper-animal-public-domainFree Image from public domain licenseD-558-2 Aircraft on lakebed. Original from NASA. Digitally enhanced by rawpixel. https://www.rawpixel.com/image/441402/free-photo-image-space-aircraft-carrierFree Image from public domain license