We present the steps taken to produce a reliable and complete input galaxy catalogue for the Dark Energy Spectroscopic
Instrument (DESI) Bright Galaxy Survey (BGS) using the photometric Legacy Survey DR8 DECam. We analyse some of the
main issues faced in the selection of targets for the DESI BGS, such as star–galaxy separation, contamination by fragmented
stars and bright galaxies. Our pipeline utilizes a new way to select BGS galaxies using Gaia photometry and we implement
geometrical and photometric masks that reduce the number of spurious objects. The resulting catalogue is cross-matched with
the Galaxy And Mass Assembly (GAMA) survey to assess the completeness of the galaxy catalogue and the performance of
the target selection. We also validate the clustering of the sources in our BGS catalogue by comparing with mock catalogues
and the Sloan Digital Sky Survey (SDSS) data. Finally, the robustness of the BGS selection criteria is assessed by quantifying
the dependence of the target galaxy density on imaging and other properties. The largest systematic correlation we find is a
7 per cent suppression of the target density in regions of high stellar density