How do I import only new photos with Image Capture.
I don't think it's entirely possible although there is an Image Capture plugin for Automator that will let you do a number of automatic procedures. I can't say if this is possible but my guess is it will be difficult. Check out the end of this article to see if this is a path you want to take. The Many Miracles of Image Capture

That kind of smart import was built into Photos (iPhoto) as a part of the OS free suite of apps. I generally use that one for easy importing and sorting but some don't because of it's odd organization and storage of the photos.