STB Lib can be found at https://github.com/nothings/stb
https://emscripten.org/docs/getting_started/downloads.html
The example was tested with 3.1.8
mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Release ..
make
./app input.jpg output.png
chmod +x build-wasm.sh
./build-wasm.sh
./build-wasm.sh Debug