Online casinos verify player identities during payment processing using a combination of Know Your Customer (KYC) procedures and advanced technology. KYC involves collecting personal information, including name, date of birth, address, and government-issued ID, which is then cross-referenced with official databases. To enhance security, some casinos also use biometric methods like facial recognition or fingerprint scanning. Additionally, they implement sophisticated fraud detection systems that monitor transaction patterns and player behavior to mitigate risks.