This is an "Inside out" backdrop image for your iMac Pro. It was made by using photos from the iFixit teardown pages. Sharp eyed viewers will notice the motherboard has been flipped around to reveal the more interesting components normally facing away from you, and the (boring) heat sinks are removed.
The blue cast was added because seeing all the components on the screen in their original colors was just too busy for day-to-day use.
Unfortunately the Photoshop source file is too large to post to GitHub (65MB). It's available on Adobe Creative Cloud if you want to tweak the appearance.