US Carriers' Stamp

This came with a small batch of stationery and permit cut-outs, purchased cheaply some time ago. It would purport to be a Carriers' Stamp, Philadelphia, Pa 1850-52 Scott 7LB13 1 cent black. But is it genuine or fake? It's a tiny stamp but I hope these images help. The back does have paper attached which may not help.
Thanks.
Daniel