1. A portable device with an image capturing capability, comprising: a semiconductor image sensor comprising a plurality of pixels; a visible light obstructer for substantially blocking visible light from impinging on the semiconductor image sensor when in place; and processing circuitry configured for: causing the semiconductor image sensor to be exposed to high-energy photons during a period of interest and while the visible light obstructer is in place; repeatedly sampling the semiconductor image sensor during the period of interest to generate a plurality of images; determining a common noise in the plurality of images; and generating a composite image from the plurality of images with the common noise substantially removed so the composite image includes image information corresponding to one or more radiated pixels of the plurality of pixels that absorbed at least some energy from one or more of the high-energy photons.