Lazy Loading

The comments have been placed here between the two images in order to push the second image further down, so that you need to scroll down to see it, unless you have a very large monitor, that is.
'Lazy loading' is a technique to make images that are outside the viewport not load until they are within the viewport. It is a way of speeding up the delivery of page contents, so only what you first see when opening a page is fully loaded, and elements further down the page will only be loaded when/if you scroll down view to them. This is especially useful if you have very long pages with a number of images. The blurred images that first appear are just mini-mini versions of the 'real' images, and they get blurred when they are blown up to the size of the real images.
Actually, what I should have done here, would have been to let the first image load normally. It is recommended that images that will be within the viewport when the page is opened, should not be lazy loading. But just for this demonstration I have not abided by that advice.

(The images are from Arendal in Norway, taken at the same time, one to the south-west where the sun had just gone down, the other facing the other way catching the coloration of the clouds.)