facebook image dimensions

I searched discussions but did not find anything about that and the manual was not helpful.

I could not find anywere a setting which dimenions my images should have at publishing on facebook. And if possible, is there a setting were I can set a watermark like for web export?

Am I stupid or isn’t there any setting for this?

Background: I like to publish some images on facebook, but many of them do have dimenions up 40 megapixel which makes them large in size, I do not want them to publish from within Aperture with that dimensions - I like to limit the dimensions to what we need for web and screen.

Any idea?