How do you tell the difference between moulting and feather pecking?

If they are moulting you do tend to see a collection of feathers in the coop.  Their comb may be paler too.  Also there is no apparent bald patch, in a partial moult it's mainly neck and a few tail feathers, in a full moult they look generally scruffy and you will see a lot of feathers around.
Hope that helps