With the escalating concern about global warming, the environmental impact of electronic devices must be scrutinized. Life Cycle Assessments (LCA) reveal that Integrated Circuits (ICs) are the primary contributors to greenhouse gas emissions in these devices. However, performing an inventory to determine the ICs impact is a complex task due to missing data and the existing studies on ICs have been neglecting CMOS Image Sensors (CIS). Despite the surge in CIS usage, particularly in smartphones, there is a lack of comprehensive models to assess their environmental impact. This paper proposes a multi-level set of models that leverage available information while considering the specificities of CIS. The most comprehensive model incorporates factors such as the total silicon area, geographical location (influencing the energy mix), and the technology node. To accommodate scenarios with incomplete data, subsequent models are designed to effectively utilize averaged parameters. The proposed models are applied to sensors manufactured by STMicroelectronics and Sony, and the results are compared with existing LCA results from Fairphone. Our approach provides a more comprehensive understanding of the environmental impact of CIS, contributing to the broader goal of reducing the carbon footprint of electronic devices. Our results suggest that the carbon impact of a Fairphone 4 image sensor is likely higher than previously estimated, with a significant gap between our findings and the expected value.