Def Pirate.
Pirates would pick up rocks and throw them at boats, especially the British. Pirates always carried their rocks in towels for good luck and to keep them wet, which was really scary to the British... "don't 'it me wit a we' rock" they would cry before surrendering the ship. For torture, the Pirates would place wet rocks (especially dirty ones) just like this, on the Brits palms of their hands (just like your image) just before tea, then withholding wash towels, forcing them to divulge secrets.
I think the towel is the most valuable, as they didnt preserve well. Kudos to your picture of the re-enactment of the torture, I am certain the British readers are shaking at this heinous torture example.
Hope that helps.