Contact photos that I have set on my iPhone appear correctly in SOGo Connector but as soon as I change anything on a contact and hit OK, its photo disappears. As a workaround, I can save the photo to my hdd before I change anything and restore it afterwards but if I forget to save a photo, it might be gone for good (the iPhone completely deletes contact photos when the server tells them there is no photo set for the contact)

My suggestion would be to either automatically backup the photos to the disk and set them as local photos or to just enter a dummy URL that SOGo Connector automatically replaces.