We can accept 1GB RAW files and 20 GB JPEG files, but this really doesn't change much in pictures.
Many-many contributors don't see why they should upload 10 MPIX photo, when they can downsample it before uploading to 0.5 MPIX. 'This is enough resolution for web publishing, isn't it?' they say.
So first step should be teaching users and then giving them 'most sophisticated file format possible (TM)' ;)
AJF/WarX