A digital camera sensor will incur pixel defects both in fabrication and during its lifetime. While manufacturing defects are corrected in the factory, in-field defects are prohibitively expensive to fix, and can eventually affect the picture quality. During the last 10 years, we have conducted a study of defect development in digital imagers, in which we had access to about 40 cameras and a database of past photos taken by them. The data we collected allows us to quantify characteristics of defect growth. Our investigations have shown that pixel defects are permanent, and their number grows with time. We found that the main type of defect is hot pixels, which are pixels that appear as a bright spot in the image even without any illumination. We also observed that the defects are distributed randomly over the sensor area and are not clustered. By studying past pictures of each given camera we found that the defect growth rate is constant over time. These spatial and temporal characteristics led us to the conclusion that defects are not likely related to material degradation or imperfect fabrication, but are caused by environmental stress such as cosmic rays radiation. Measuring the effect on the defect rate of sensor parameters such as sensor area, number of pixels, pixel size, and sensor technology (CCD Charge Coupled Device vs. APS – Active Pixel Sensor) yielded a power law, implying that increasing the number of pixels by shrinking the pixel size will result in a higher defect rate and is, therefore, not recommended.