Image formats arsd.image can load (except Unknown, of course).
Try to guess image format from file extension.
Try to guess image format by first data bytes.
Try to guess image format from file name and load that image.
Try to guess image format from data and load that image.
You should either copy the image.d module and the pieces you use to your own project, or always use it along with the rest of the repo and dmd -i, or the dub arsd-official:image_files subpackage, which both will include new files automatically and avoid breaking your build.
The image resize code used to live directly in here, but has now moved to a new module, arsd.imageresize. It is public imported here for compatibility, but the build has changed as of December 25, 2020.
This file imports all available image decoders in the arsd library, and provides convenient functions to load image regardless of it's format. Main functions: loadImageFromFile and loadImageFromMemory.