Mid 2007 20" iMac — Faint vertical lines on display, is this a serious problem? I was given an old iMac to toy around with. Its working well, but it has faint vertical lines on the display visible on solid colors. I've done some googling and haven't found an answer exactly what this is.

Attached is a pic I took with a camera. The vertical lines are most visible in the black space on the bottom right. 


 The lines in the white space are something my camera picked up, not a problem.

Is there any way to stress test this and determine the stability and/or seriousness of these artifacts?
I wouldn’t be concerned you could use the Mac for a week and then note for yourself if the situation is stable or if you want to start saving money to get it repaired.  We have machines like that that we use for timeclocks of people punching in/out - they’ve  been stable for years with graphics glitches similar to that. 

Keep toying around and figuring out how you can make the best use of this regift it would be my advice. I wouldn’t spend any money repairing it.  Save your budget so you could buy a new display if you actually need one.  Get one that would work with both the Mac and a low-cost computer like a raspberry pi.