Any donation using a Web site and QR code will eventually create a tax liability for your homeless friend along with the obligation to share a percentage of any incoming donations with Paypal or similar companies, but the real challenge will be to convince a bank to open an account to withdraw funds. I also feel that a homeless using QR code and a Website to promote itself could be ill-perceived as a marketing strategy rather than as a mean to survive, although your intentions to help this person are very noble and sincere.