It depends on the size of the photo and the speed of your internet connection.
If you are using a really big photo (say 10mb its going to take about 5 minutes to upload) Be patient it will work, there is no upper limit.
It's better if your photo image size is not that large, anything above 1mb should be good enough quality.
Speed of Connection:
If possible try and upload your photos where you have fast internet connection speeds. If this isn't possible, it will still work, but might take longer for each photo to upload.
If you're waiting longer than 5 minutes and the photo hasn't uploaded, most likely something has gone wrong. You should quit your browser and log back in and try again.