Photometry measurement method with Gnuastro: example of a stream around ESO 285-042. left:r band background-subtracted input image; centre: apertures tracing the stream in which photometry parameters, such as magnitude, surface brightness and colours are measured (image resampled to a pixel size 4 × 4 larger than the input image); right: image with a masked central galaxy, as well as foreground and background sources.