I have never done that intentionally.
So I gave it a try.
Remember to turn off your flash.
I have a 22" Dell monitor and used a Canon A570IS camera.
I selected a colorful photo of my own and displayed it full size on the PC screen.
I placed the camera lens so near to the PC screen that the picture filled the camera LCD screen.
Every shot (no matter what setting was used) had very strong herringbone patterns throughout the photo.
So I backed up so that the camera lens was 3 feet from the PC Monitor.
No more herringbone pattern.
The photo looked good (maybe a bit brighter than what I was seeing on the PC monitor.
Colors were good.
With the camera in Auto mode, the camera settings were 1/16th shutter speed, f2.6 aperture and ISO setting of 200.
That means you need to be using a tripod to support the camera to prevent blurring due to camera movement.
It is not practical for any type of serious photography.
I try to snap photos off the PC's LCD screen. Sometimes the results are fine while other times, the colors are bluish and scanning lines appear which ruin the snapshots. Any advice?