At the well Locke's 'eye' scar moves from one cheek to another. When first trying to climb into well it moves to his left cheek.

Will find links if I can.

Blunder or Easter Egg?
100%
Here's the links:

http://gallery.lost-media.com/displayimage-1466-397.html

and

http://gallery.lost-media.com/displayimage-1466-413.html

They probably reversed the image in the second one for some reason, blooper.

They probably just flipped the image. They do it a lot. With Locke it looks more evident due to his scar.