I don't think the only potential problem here is the 100-400, use of filters, or lack of lens hoods. On my last two trips I've had images with ghosting like this from both the 400 f5.6 and 500 f4L IS--no filters (other than the one built in to the 500), lens hoods always used. I discussed it with Canon yesterday, and it sounded as if they've had other ghosting reports. The technician I spoke with mentioned reflections from water as a possible factor, and indeed, the images where I've noticed ghosting (mostly flights shots) were all shot from a shore or ship. Since at least two lenses were affected, I suspect the camera (1Ds mark III). I sent a sample image, hope to know more today.