Percival Lowell. Reproduction of pastel drawing after N. Priest, 1910. https://www.rawpixel.com/image/14010999/percival-lowell-reproduction-pastel-drawing-after-priest-1910Free Image from public domain licenseJongens bij een man met schaatsijzers (1887 - 1916) by Willem Pothast https://www.rawpixel.com/image/13791607/jongens-bij-een-man-met-schaatsijzers-1887-1916-willem-pothastFree Image from public domain licenseThe shooting down of a German dirigible over London by H Scott Orr https://www.rawpixel.com/image/14279937/the-shooting-down-german-dirigible-over-london-scott-orrFree Image from public domain license