system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do image file sizes differ if the lens and camera are the same?
gpt
Images are compressed. Compression depends on the contents, some content can be more easily compressed than other content.

This is because compression works mainly by removing repetitions in the data, so if the data has lots of repetitions (for example if the image is just a big black square) then it is easier to compress, resulting in a smaller file.