It is a feature that most of the developers ignore. It should be seen as part of the functionality.
Image/file upload should always have a progress bar. The users cannot sit in the dark and keep guessing about the background progress.
When the user requests the server to perform some operation, it is good to show them about the progress. It is a good UI/UX behavior. The progress bar is one of the best ways to show the status of the in-progress operation.
Get started with jQuery Ajax Image Upload Animating Progress Bar with my simple Ajax Widget