* You can open your network section in dev tools, for see how images are loading
picture-01.jpg media="(min-width: 1280px)" picture-02.jpg media="(min-width: 980px)" picture-03.jpg media="(min-width: 320px)"
picture-04.jpg media="(min-width: 1280px)" picture-05.jpg media="(min-width: 980px)" picture-06.jpg media="(min-width: 320px)"
picture-07.jpg media="(min-width: 1280px)" picture-08.jpg media="(min-width: 980px)" picture-09.jpg media="(min-width: 320px)"
* You can open your network section in dev tools, for see how background-images are loading
Single Background Image
Multiple Background Images Check the console to see that these are indeed separate images.
Multiple Background Images Fallback Method ( where the first / foremost image fails ) Check the console to see that the first image is failed to load.
Responsive Background Images set Change a device pixel ratio with devtools and check the console to see which image dimension was loaded
video courtesy of Big Buck Bunny.
normal video example