Nicole Bailey, 23, picked up the note in a shop and slipped it into her pocket, not imagining she was breaking the law.
She ended up in court after CCTV cameras caught her with the note a customer had dropped.
Police have warned 'finders keepers' doesn't apply, and it's a crime to keep money or goods someone else has lost.
Magistrates at North Staffordshire Justice Centre heard the cash had been withdrawn shortly beforehand by a fellow customer at the One Stop store in Blurton, Stoke-on-Trent.
This is stupid to charge someone of a petty crime and not convict murderers.
Any signs will be appreciated!