Continuing to tweak my phone I tried out High Contrast mode earlier yesterday.
Later on I then tried to use FB photo's for my lock screen...the photo's didn't show however if I held power button until the "power off" screen drops in the pictures were on there.
Same for CNN app on lock screen.
After restarting and trying a few times I have discovered that if I have High Contrast mode turned on it stops the lock screen from displaying the dynamic photo's from FB / CNN / Bing.
Not sure if this is intended or a bug but thought i'd share in case others get frustrated like I was.
Guess I have to decide between high contrast and lock screen photos for now.