I bought the PC around a year and a half ago. It has never really displayed a problem before now.
I have never used a screen saver, so I don't believe that has anything to do with it, and no I haven't changed the dimensions of the images, if I wanted a "workaround", I would have simply done that and not come here for help. I want a solution.
Welcome to the forum KokoMats. In this forum we try to be
courteous to those who are simply trying to help us solve our problems. Yes, of course you want a solution, but in the meantime, sometimes a workaround can temporarily allow you to do what you are trying to do while you are searching for an actual solution. (And sometimes there is NO solution -- so you're stuck with a workaround, or nothing.)
In regard to my screensaver suggestion --- whether or not you USE a screensaver is irrelevant --- the sizes of your images can be changed in a NUMBER OF WAYS -- one of which is through the back door, i.e. by changing the photo dimensions in the Pictures folder via the Screensaver Settings app.