ISON image from the 1.52 m telescope at Sierra Nevada Observatory taken on February 2013, 14.04 UT. Upper four panels: unfiltered image (upper left) and filtered images using different digital techniques: low Pass, Larson-Sekanina, and Laplacian filters (Samarasinha & Larson 2014). Green circles mark the comet photocentre. Green arrows indicate the small tail or coma enhancement structure pointing to the antisolar direction, clearer in the filtered images, in particular in the Larson-Sekanina and Laplacian ones. Bottom panel: zoom-in of the ISON image processed with the Laplacian filter. Blue circles are the different apertures (diameter in arcseconds) used to perform the photometry. The smallest (aperture = 5.6′′) is not contaminated by the small antisunward tail or coma structure. In all panels north is up and east to the left. The antisolar direction is shown with a black arrow.