This paper presents a review of energy harvesting image sensor designs in CMOS technology. Two CMOS image sensors with on-chip energy harvesting capability are presented. Quantitative comparison of power generation capacity of these two different topologies is provided. Both structures make use of the photoelectric conversion capability of the photodiode pixel array and reconfigure the array to harvest the solar energy. The first pixel is an N-well type pixel while the second structure is an isolated P-well type pixel. Both structures were fabricated and measurement results are presented in this paper.