If you leave the page open, the image will not update by itself. You need to reload the page/image, then the data will update.
That makes sense. Nobody would expect images posted on a forum to update without reloading the page.
But it would be nice if the timestamp can also be displayed. That would remove the doubts for someone who just reads the whole context without knowing how the thing works.
I would not ignore the purpose of this without an update after each refresh. There are situations where it is necessary to know the value at the time of writing the post.