I'm sure that many of us have used Google photos high quality backup which allows us to store photos online without fees.
Recently, I thought of testing just how high quality the uploads really were by uploading some pics (below 16 MP) and comparing them to the original in terms of resolution, quality (as seen by the eye) and file size.
I was surprised to note that the resolution and quality were almost the same as the original (no visual difference to the eye even zoomed in in most cases) but the file size was drastically reduced -- at least 2-3x and even around 10x in some cases. Having used RAR for various types of files in the past, I knew that it wouldn't come close and didn't bother to test it.
The question is : How does Google manage such great compression without any noticeable change in the image itself? Are they dumping location data or other data related to the image that the amateur photographer doesn't know of?