Suggest some kind of small personal storage space for each user that can hold 1 or 2 images for a temporary amount of time, that other users can upload into. This would allow users to transfer images to eachother that they are working on as a group, or need help on, or a rework for, etc.
Email attatchments and private hosting over and over can become a chore, it would just make things easier for the user and harder for caedes :)