responsive notification page using react

Hello everyone. I heard that the putting your project images in the src folder makes them faster to load. but when I build my project and deploy it somewhere like netlify, no image will load but when I put my assets folder in the public folder and build again everything will work fine. I want to know the reason of that??

also I have had some projects that putting images in the src folder will work just fine. I am confused. why sometimes it works and sometimes not??