While this is happening try and click the upload button again. This might 'force' your picture to upload. If this doesn't help then close the picture capsule. Save your hub without publishing it then go back into your hub by editing it. Open the picture capsule and try to upload the picture again. This usually solves the problem for me.
Do this procedure also for when you add a photo capsule and for some reason the hubpage screen scrolls straight up to the top of the screen. I always have to go out then come back and re-edit the hub.