I have spent a lot of time at CODEX reading about images and galleries but I still have no understanding of how images work and interact on WordPress.
You upload a file. It automatically creates a whole lot of other files. I understand this is for serving the right size file for the right thing.
I my case, for every single file I upload, the backend will reproduce 8 different files with pixel dimensions listed in the file name. Also, some of these pictures are cropped awkwardly and not reflective of the original image.
1) Why does it do this? How is it used? What controls this? The theme? How can you control how many are created, and those dimensions?
2) If I want to recreate the images with more compression, why can't I simply replace the file via FTP. (I have over 100 files to fix and it is time consuming to replace ALL of them individually.)
I've tried to do this and it didn't give me the results I expected. I got broken thumbnails. So I reuploaded the file and ended up with all the copies. ARGH.
A good resource that really explains how it works would be great.