In some cases, yes. Nearly all online casinos have a full account verification process, mostly avoided at registration for a better customer experience and usually requested when deposits or withdrawals reach a certain threshold as part of their licence obligations. Expect to complete Know Your Customer (KYC) verification at some stage with most online casinos to verify your identity by submitting requested documentation such as photographic ID or proof of address. Under Anti Money Laundering (AML) obligations, some casinos are required to follow a trail to the Source Of Wealth (SOW) to verify funds by checking bank statements and wage slips or similar. There are some online casinos whose terms and conditions state that winnings will not be paid until these requirements have been met.