Yes and no. You can report finds and get a reward in most countries but you might risk incriminating yourself at the same time in countries where metal detector

Yes and no. You can report finds and get a reward in most countries but you might risk incriminating yourself at the same time in countries where metal detectors are banned. If it is a one off you are fine, but if you go around finding tons of coins all over the country and reporting them it will look suspicious.