In Forza's built-in screenshot system or when you press the Xbox button and then press Y?It won't allow me to save pictures anymore, so I guess I need to figure that out.
Finished off Fortune Island a few days ago...that last chest was a fun one lol.
If it's the first, I had that problem in FH3 too. I think it only allows you to save some 100+ photos. I just use Y right now. You don't get the watermark and there seems to be no limit to the photos you can take.