I've noticed a black line on my desktop, and I can't seems to figure out how to remove it. I've restarted my computer several times, relaunched my Finder through "Force Quit," and searched through my application to remove anything I don't use anymore. I don't think it's a display card issue because I'm able to move applications behind it, and they would still appear, but just with the line in front of it. I take really good care of my laptop, so I don't think it's due to external damage. And, my cursor can move over the line. If it helps, I have a MacBook Pro (15-inch, Mid 2012) and using version 10.13.6 of macOS High Sierra. If anyone could help me, I'd greatly appreciate it.
[UPDATE: The image is a screenshot and the bar disappeared with a pixel checking program, but still there after changing the desktop picture and adjusting the display profile.]