libgdlibpng
Just run make to build the pngsplash binary, you can copy it to any path to it can be executed e.g. /usr/bin/pngsplash.
Just run pngsplash with the path to your image as the first argument, e.g.:
pngsplash /usr/share/pngsplash/splash.png
This should run as early as possible and it is recommended to disable any kind of logging during boot that writes to the frame buffer e.g. quiet splash, you may also need to change other options in cause of custom kernels.
pngsplash Copyright (C) 2021 Torsten Braun
This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.