Detect JPEG image quality

Question

I allow users to upload images. However, I want to keep JPEG quality not more than 90%. What I plan to do is to detect the current quality: - If less than 90% do nothing - If mo

Answer 1

You cannot guarantee that the quality setting is stored in the JPEG's metadata. This is an encoder setting, not an image attribute.

Read more here about estimating JPEG quality

It might make more sense to simply define a maximum file size. At the end of the day, restricting image quality is all about saving bandwidth. So setting a ratio between image dimensions and file size is more appropriate.