My ranking of the APIs of various image decoding libraries:
1. stb_image tier: libwebp
Call a function. You're done.
2. Good tier: libheif (also handles avif)
A bunch of functions you need to call in sequence, all presented as a neat and short program in the README.
3. Okay tier: libpng, libjpeg.
You have to go through a narrated guide on what to call. You can get the work done, but you have to wade through super important stuff like low-quality decoding in case you want to run on Amiga.