I had the same issue with my original N5. After in depth troubleshooting, it was determined a hardware issue. Swapped for my 2nd N5. Same issue. Swapped for my 3rd N5, same issue. Shows more with some photos, less with some. Only happens when photo is set as wallpaper. It shows on homescreen and on lock screen. When viewing same image in gallery, there are no lines visible. When saving a screenshot and viewing on another device or conputer, lines are visible. Also noticed that when using a pure white wallpaper, Samsung has added a hideous fade on the top and bottom of the display. Why they did this is beyond me. Looks horrible.