Base URL:
https://raw.githubusercontent.com/BANKEX/Tokens/master/tokenImages/<contract_address_prefix>/<contract_address>.png
where contract_address_prefix is first 3 letters from contract address including leading 0x, f.e. 0x4.
Example (BKX Token):
https://raw.githubusercontent.com/BANKEX/Tokens/master/tokenImages/0x4/0x45245bc59219eeaaf6cd3f382e078a461ff9de7b.png