I have found this tool that optimizes images for the web. What is surprising for me (of course, there will be other tools like this :)) is that it only optimizes the uploaded image if it is possible, I mean, if it considers that the image is already optimized for the web it says "No savings".
My question: before running something like
convert -quality 80, is there any way (using ImageMagick or any other tool in Linux) to ckeck if an image is already optimized for the web? In that case I would not run
convert -quality 80.