We report a novel hardware method for generating authentication keys based on a physically unclonable function (PUF) of a perimeter-gated single photon avalanche diode (pg-SPAD) imager. We tested three 64 × 64 pg-SPAD imagers over a temperature range extending from 27◦C to 75◦C and demonstrated that authentication keys can be generated with quantifiable difference and that they are resilient to temperature change. We used the imager’s spatial dark count variation as a PUF, i.e., as a means to generate unique hardware fingerprints on which the keys are based. Without applying complex key generation algorithms or temperature compensation techniques, we obtained approximately 0.1 in average normalized Hamming distance (nHD) between intra-chip keys generated from the same challenge and approximately 0.5 in average nHD between intra-chip keys generated from different challenges. Inter-chip keys generated with the same challenge also showed sufficient differentiation, i.e., a nHD of approximately 0.5. Additionally, we demonstrate that perimeter gating offers an additional security feature as it can either alter or obfuscate the imager’s PUF.