How do they know? Well just LOOK at the GRID in those clouds, LOL... Checkmate Globers!
Look at similarly compressed cloud JPGs from just about ANY source. Here is an aerial image from A flight to Paraguay - you can see the SAME grid behavior because THIS IS PART OF HOW JPG COMPRESSION WORKS. I've saved these in .png to avoid further artifacting but you can get the originals and see the same things by zooming in using an appropriate image viewing tool.
If you want to show an image is a fake you need to go find the ORIGINAL uncompressed RAW/TIF data for that image and PROVE it's a fake. Showing me JPG artifacts in a JPG image doesn't prove anything is a fake.
Here is a good resource for that -- they are hosting hundreds of thousands of images here:
Try 'ISS039-E' for a start -- that's almost 12K images.
Recommend getting GIMP to edit RAW files.