Every day Déjà Dup backups it needs a long time because of my Pictures-folder. Is there a possibility to force Déjà Dup to backup only new and changed files?
As far as I recall, Déjà-Dup will only do incremental updates. Therefore what you are asking for, is exactly what it does already. I'd guess that syncing and comparing just takes a long time. If you want to restore a file via Déjà-Dup from UbuntuOne for example, it will take ages.