You're good mate. I meant exaclty what aprilnya said. I thought you are using the Lambda just to validate the 10mb limit - and just for that you don't need the lambda :) and could save yourself some cents & effort.
But if you do resizing as well, then ofc you need the Lambda (or some other compute engine).
But if you do resizing as well, then ofc you need the Lambda (or some other compute engine).