ETSI reduces imaging data from the Exoplanet Transmission Spectroscopy Imager by co-adding raw exposures and extracting aperture photometry. The pipeline reads raw FITS and non-FITS images, constructs or propagates basic header information such as observation time, airmass, and exposure time, groups exposures into time-based co-adds, and writes combined images with co-add metadata. For photometry, ETSI can optionally align images to a reference frame, refine hand-selected stellar positions by centroiding, and measure fluxes with elliptical apertures together with sky-background estimates and flux uncertainties. It outputs per-star light-curve files containing times, exposure information, airmass, image-level sky statistics, and, for each configured aperture, the measured flux, uncertainty, centroid positions, and background value.