If you take a look at sites like this one
you'll see that their .jpgs load unconventionally, starting with a pixelated version and slowly increasing in resolution instead of loading from top to bottom.
In inspector, the images don't look special to me. Is this a certain way of indexing the file itself so the browser receives data in this specific order?
Best How To :
I've seen this effect on other websites as well. This depends on the image type you are saving it as. According to Wikipedia:
Interlacing (also known as interleaving) is a method of encoding a bitmap image such that a person who has partially received it sees a degraded copy of the entire image. When communicating over a slow communications link, this is often preferable to seeing a perfectly clear copy of one part of the image, as it helps the viewer decide more quickly whether to abort or continue the transmission.
This is known as interlacing for PNG and GIF type images, and a progressive format for JPEG images.
There is an option in the
Save for Web... section in Photoshop: