Yeah, the image file still needs to live somewhere. Obsidian’s plain text files differ from e.g., Word .docx files—they literally can’t contain other media, only text.
I rarely use images, so I’m probably not qualified to comment on best practice. I think you’ll find folks have varying opinions on this, though, so “do what currently feels right” is probably the right advice.
For what it’s worth, I do like naming files of all kinds. It might not matter in the moment, but it’ll matter after several months have passed and you’re looking for it again. So, I name everything as descriptively and search-friendly as possible.
If you rename a file that has been linked in the Obsidian app, Obsidian will fix the links you’ve added to your notes for you. However, if you rename a file outside the Obsidian app (e.g., in Finder/File Explorer), you will need to make sure to correct the links yourself.