When you select an image to use with a component, a unique copy is created and stored with the site.
When you upload files, they are stored in the site repository. If you upload a file with the same name as an existing file, it creates a new version of the file.
The image file you see on the page is a copy of the file selected from the repository and is not automatically updated. This is by design and prevents inadvertent changes in existing pages when an image file is updated in the repository.
To update the image used with the component, you must explicitly select the image from the component property page. See Images for details.