We need to specify hashes for `libpng-1.3` and `libjpeg-4.6` right? Is there tooling to fill-out them automatically? How to find out what versions of `libpng`

We need to specify hashes for `libpng-1.3` and `libjpeg-4.6` right? Is there tooling to fill-out them automatically? How to find out what versions of `libpng` are available to be used in `shell.nix` or `shell.flake` with nix tools?