Question: Strange rectangles on desktop background
My MacBook Pro's desktop background has these strange rectangles that I've never seen before. At first I thought it was showing up in the image itself but it's still there when I change to different desktop images. It's not a screen display issue because I can cover it up with windows like Finder and Firefox. I can't drag or do anything to the shapes.
Has anyone else had this issue? Does anyone know a solution? Here are some screenshots to show what I'm talking about.
Original desktop background, rectangles in lower-right section:
With a basic color background:
Clicking the background and highlighting over the rectangles doesn't affect them:
With a stock background image:
Covering the rectangles with the Finder window:
MacBook Pro, macOS High Sierra (10.13.3)